Add GitHub actions workflow for testing CMake build of examples directory

I confirmed that this test would catch the problem from #12450.

PiperOrigin-RevId: 526165526

.github/workflows/test_cpp.yml

@@ -200,6 +200,37 @@ jobs:
               ctest --verbose --parallel 20;
               ccache -s'
 
+  linux-cmake-examples:
+    name: Linux CMake Examples
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout pending changes
+        uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+        with:
+          ref: ${{ inputs.safe-checkout }}
+          submodules: recursive
+
+      - name: Setup ccache
+        uses: protocolbuffers/protobuf-ci/ccache@v1
+        with:
+          cache-prefix: linux-cmake-examples
+
+      - name: Run tests
+        uses: protocolbuffers/protobuf-ci/docker@v1
+        with:
+          image: us-docker.pkg.dev/protobuf-build/containers/test/linux/cmake@sha256:e0eb6c69b7551d89f0dbdbe11906077a1d501229c28db39623b945e0c5d7029a
+          credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
+          command: >-
+            /install.sh -DCMAKE_CXX_STANDARD=14 ${{ env.CCACHE_CMAKE_FLAGS }} \&\&
+            cd examples \&\&
+            mkdir build \&\&
+            cmake
+            ${{ env.CCACHE_CMAKE_FLAGS }}
+            -Dprotobuf_BUILD_PROTOBUF_BINARIES=OFF
+            -DCMAKE_CXX_STANDARD=14
+            -S . -B build \&\&
+            cmake --build build
+
   non-linux:
     strategy:
       fail-fast: false   # Don't cancel all jobs if one fails.