Fix CLOUDSDK_PYTHON env var on Windows in tests

The setting of these env vars was recently updated to use the new syntax. This does not work as-is on powershell due to encoding, as documented here:
https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#environment-files

To fix this, execute this using bash.

Author: anonymous-akorn

.github/workflows/cpp-packaging.yml

@@ -663,6 +663,7 @@ jobs:
     # Workaround for https://github.com/GoogleCloudPlatform/github-actions/issues/100
     # Must be run after the Python setup action
     - name: Set CLOUDSDK_PYTHON (Windows)
+      shell: bash
       if: runner.os == 'Windows' && !cancelled()
       run: echo "CLOUDSDK_PYTHON=${{env.pythonLocation}}\python.exe" >> $GITHUB_ENV
     - name: Install Cloud SDK

.github/workflows/integration_tests.yml

@@ -123,6 +123,7 @@ jobs:
       # Workaround for https://github.com/GoogleCloudPlatform/github-actions/issues/100
       # Must be run after the Python setup action
       - name: Set CLOUDSDK_PYTHON (Windows)
+        shell: bash
         if: startsWith(matrix.os, 'windows') && !cancelled()
         run: echo "CLOUDSDK_PYTHON=${{env.pythonLocation}}\python.exe" >> $GITHUB_ENV
       - name: Install Cloud SDK