Fix windows 2019 build.

setup-gcloud doesn't honor the environment variables set by setup-python, so we need to manually set CLOUDSDK_PYTHON before running it.

PiperOrigin-RevId: 578674246

.github/workflows/test_cpp.yml

@@ -366,6 +366,7 @@ jobs:
               -Dprotobuf_BUILD_EXAMPLES=ON
             vsversion: '2019'
             cache-prefix: windows-2019-cmake
+            # windows-2019 has python3.7 installed, which is incompatible with the latest gcloud
             python-version: '3.8'
           - name: Windows CMake 32-bit
             os: windows-2022
@@ -399,13 +400,6 @@ jobs:
           ref: ${{ inputs.safe-checkout }}
           submodules: recursive
 
-      - name: Install Python
-        if: ${{ matrix.python-version }}
-        uses: actions/setup-python@61a6322f88396a6271a6ee3565807d608ecaddd1 # v4.7.0
-        with:
-          python-version: ${{ matrix.python-version }}
-          cache: pip
-
       - name: Setup MSVC
         if: ${{ runner.os == 'Windows' }}
         uses: ilammy/msvc-dev-cmd@cec98b9d092141f74527d0afa6feb2af698cfe89 # v1.12.1
@@ -413,6 +407,17 @@ jobs:
           arch: ${{ matrix.windows-arch || 'x64' }}
           vsversion: ${{ matrix.vsversion }}
 
+      # Workaround for incompatibility between gcloud and windows-2019 runners.
+      - name: Install Python
+        if: ${{ matrix.python-version }}
+        uses: actions/setup-python@61a6322f88396a6271a6ee3565807d608ecaddd1 # v4.7.0
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Use custom python for gcloud
+        if: ${{ matrix.python-version }}
+        run: echo "CLOUDSDK_PYTHON=${Python3_ROOT_DIR}\\python3" >> $GITHUB_ENV
+        shell: bash
+
       - name: Setup sccache
         uses: protocolbuffers/protobuf-ci/sccache@v2
         with: