Automerge version bumps

This change marks PRs created by `cockroach-teamcity` ready to be merged
after all checks are passed.

.github/workflows/automerge.yaml

@@ -0,0 +1,26 @@
+name: Automerge version bumps
+
+on:
+  pull_request:
+    branches: [ master ]
+    paths: 
+    - "!**"
+    - "Formula/*"
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  automerge:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor == 'cockroach-teamcity' }}
+    steps:
+      - name: Approve a PR
+        run: gh pr review --approve "${{github.event.pull_request.html_url}}"
+        env:
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      - name: Enable auto-merge
+        run: gh pr merge --auto --merge "${{github.event.pull_request.html_url}}"
+        env:
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}