Auto-merge Google API changes.

Don't merge all possible dependency changes, only the ones coming from
dependabot and for Google APIs. The rest still needs manual merges.

This should alleviate the burden of reviewing these every week.

.github/workflows/dependabot-automerge.yml

@@ -0,0 +1,26 @@
+name: Dependabot auto-merge
+on: pull_request
+
+permissions:
+  contents: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        safe-dependency:
+          - "google.golang.org/api"
+    if: ${{ github.actor == 'dependabot[bot]' }}
+    steps:
+      - name: Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v1.1.1
+        with:
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
+      - name: Enable auto-merge for Dependabot PRs
+        if: ${{contains(steps.metadata.outputs.dependency-names, matrix.safe-dependency)}}
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}