diff --git a/.github/workflows/ci_sh_def.yml b/.github/workflows/ci_sh_def.yml
index b9cb57a05..a799012d0 100644
--- a/.github/workflows/ci_sh_def.yml
+++ b/.github/workflows/ci_sh_def.yml
@@ -96,6 +96,9 @@ jobs:
 
     - name: Update CMake
       uses: jwlawson/actions-setup-cmake@v1.13
+      # TEMPORARILY pin version because 3.26.0-rc1 is failing under macOS:
+      with:
+        cmake-version: '3.25.2'
 
     - name: Cache wheels
       if: runner.os == 'macOS'
@@ -297,6 +300,8 @@ jobs:
           - dev
         std:
           - 11
+        container_suffix:
+          - ""
         include:
           - clang: 5
             std: 14
@@ -310,9 +315,12 @@ jobs:
             std: 20
           - clang: 14
             std: 20
+          - clang: 15
+            std: 20
+            container_suffix: "-bullseye"
 
     name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
-    container: "silkeh/clang:${{ matrix.clang }}"
+    container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
 
     steps:
     - uses: actions/checkout@v3
@@ -784,7 +792,7 @@ jobs:
       uses: jwlawson/actions-setup-cmake@v1.13
 
     - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.12.0
+      uses: ilammy/msvc-dev-cmd@v1.12.1
       with:
         arch: x86
 
@@ -838,7 +846,7 @@ jobs:
       uses: jwlawson/actions-setup-cmake@v1.13
 
     - name: Prepare MSVC
-      uses: ilammy/msvc-dev-cmd@v1.12.0
+      uses: ilammy/msvc-dev-cmd@v1.12.1
       with:
         arch: x86
 
@@ -1093,6 +1101,9 @@ jobs:
 
       - name: Update CMake
         uses: jwlawson/actions-setup-cmake@v1.13
+        # TEMPORARILY pin version because 3.26.0-rc1 is failing under macOS:
+        with:
+          cmake-version: '3.25.2'
 
       - name: Run pip installs
         run: |
diff --git a/.github/workflows/ci_sh_def.yml.patch b/.github/workflows/ci_sh_def.yml.patch
index 2dfb52fd3..d780bee9c 100644
--- a/.github/workflows/ci_sh_def.yml.patch
+++ b/.github/workflows/ci_sh_def.yml.patch
@@ -1,5 +1,5 @@
---- ci.yml	2023-01-03 19:40:01.489281529 -0800
-+++ ci_sh_def.yml	2023-01-03 19:40:50.224704081 -0800
+--- ci.yml	2023-02-07 23:54:04.279545875 -0800
++++ ci_sh_def.yml	2023-02-07 23:54:24.677604204 -0800
 @@ -1,4 +1,16 @@
 -name: CI
 +# PLEASE KEEP THIS GROUP OF FILES IN SYNC AT ALL TIMES:
@@ -27,7 +27,7 @@
    cancel-in-progress: true
  
  env:
-@@ -114,6 +126,7 @@
+@@ -117,6 +129,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=11
@@ -35,7 +35,7 @@
          ${{ matrix.args }}
  
      - name: Build C++11
-@@ -143,6 +156,7 @@
+@@ -146,6 +159,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=17
@@ -43,7 +43,7 @@
          ${{ matrix.args }}
  
      - name: Build
-@@ -164,6 +178,7 @@
+@@ -167,6 +181,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=17
@@ -51,7 +51,7 @@
          -DPYBIND11_INTERNALS_VERSION=10000000
          "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
          ${{ matrix.args }}
-@@ -251,6 +266,7 @@
+@@ -254,6 +269,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=17
@@ -59,7 +59,7 @@
  
      - name: Build
        run: cmake --build build -j 2
-@@ -311,6 +327,7 @@
+@@ -319,6 +335,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DCMAKE_CXX_STANDARD=${{ matrix.std }}
@@ -67,7 +67,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -340,7 +357,7 @@
+@@ -348,7 +365,7 @@
        run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
  
      - name: Configure
@@ -76,7 +76,7 @@
  
      - name: Build
        run: cmake --build build -j2 --verbose
-@@ -420,7 +437,7 @@
+@@ -428,7 +445,7 @@
          cmake3 -S . -B build -DDOWNLOAD_CATCH=ON \
                              -DCMAKE_CXX_STANDARD=11 \
                              -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
@@ -85,7 +85,7 @@
                              -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp"
  
      # Building before installing Pip should produce a warning but not an error
-@@ -479,6 +496,7 @@
+@@ -487,6 +504,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DCMAKE_CXX_STANDARD=${{ matrix.std }}
@@ -93,7 +93,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -534,6 +552,7 @@
+@@ -542,6 +560,7 @@
          -DDOWNLOAD_CATCH=ON     \
          -DDOWNLOAD_EIGEN=OFF    \
          -DCMAKE_CXX_STANDARD=11             \
@@ -101,7 +101,7 @@
          -DCMAKE_CXX_COMPILER=$(which icpc)  \
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
-@@ -566,6 +585,7 @@
+@@ -574,6 +593,7 @@
          -DDOWNLOAD_CATCH=ON     \
          -DDOWNLOAD_EIGEN=OFF    \
          -DCMAKE_CXX_STANDARD=17             \
@@ -109,7 +109,7 @@
          -DCMAKE_CXX_COMPILER=$(which icpc)  \
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
-@@ -633,6 +653,7 @@
+@@ -641,6 +661,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=11
@@ -117,7 +117,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -683,6 +704,7 @@
+@@ -691,6 +712,7 @@
          cmake ../pybind11-tests
          -DDOWNLOAD_CATCH=ON
          -DPYBIND11_WERROR=ON
@@ -125,7 +125,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
        working-directory: /build-tests
  
-@@ -778,6 +800,7 @@
+@@ -786,6 +808,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
@@ -133,7 +133,7 @@
          ${{ matrix.args }}
      - name: Build C++11
        run: cmake --build build -j 2
-@@ -832,6 +855,7 @@
+@@ -840,6 +863,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
@@ -141,7 +141,7 @@
          ${{ matrix.args }}
      - name: Build C++11
        run: cmake --build build --config Debug -j 2
-@@ -872,6 +896,7 @@
+@@ -880,6 +904,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=20
@@ -149,7 +149,7 @@
  
      - name: Build C++20
        run: cmake --build build -j 2
-@@ -919,7 +944,7 @@
+@@ -927,7 +952,7 @@
      - name: Configure C++11
        # LTO leads to many undefined reference like
        # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
@@ -158,7 +158,7 @@
  
      - name: Build C++11
        run: cmake --build build -j 2
-@@ -937,7 +962,7 @@
+@@ -945,7 +970,7 @@
        run: git clean -fdx
  
      - name: Configure C++14
@@ -167,7 +167,7 @@
  
      - name: Build C++14
        run: cmake --build build2 -j 2
-@@ -955,7 +980,7 @@
+@@ -963,7 +988,7 @@
        run: git clean -fdx
  
      - name: Configure C++17
@@ -176,7 +176,7 @@
  
      - name: Build C++17
        run: cmake --build build3 -j 2
-@@ -1022,6 +1047,7 @@
+@@ -1030,6 +1055,7 @@
            -DDOWNLOAD_EIGEN=ON
            -DCMAKE_CXX_COMPILER=clang++
            -DCMAKE_CXX_STANDARD=17
@@ -184,7 +184,7 @@
  
        - name: Build
          run: cmake --build . -j 2
-@@ -1087,6 +1113,7 @@
+@@ -1098,6 +1124,7 @@
            -DDOWNLOAD_EIGEN=ON
            -DCMAKE_CXX_COMPILER=clang++
            -DCMAKE_CXX_STANDARD=17