ci: auto-merge the pending release PR on the weekly run

.github/workflows/release.yml

@@ -26,6 +26,54 @@ jobs:
         id: release
         uses: googleapis/release-please-action@45996ed1f6d02564a971a2fa1b5860e934307cf7
 
+  merge-release-pr:
+    name: Merge Release PR
+
+    runs-on: ubuntu-latest
+
+    needs: [release-please]
+
+    if: github.event_name == 'schedule' && needs.release-please.outputs.releases_created != 'true'
+
+    permissions:
+      actions: write
+      contents: write
+      pull-requests: write
+
+    env:
+      GH_TOKEN: ${{ github.token }}
+      GH_REPO: ${{ github.repository }}
+
+    steps:
+      - name: Find pending release PR
+        id: pr
+        run: |
+          gh pr list --state open --label "autorelease: pending" --json number,headRefName,headRefOid \
+            --jq '.[0] // empty | "number=\(.number)\nbranch=\(.headRefName)\nsha=\(.headRefOid)"' >> "$GITHUB_OUTPUT"
+
+      # Pushes made with GITHUB_TOKEN don't trigger CI, so dispatch it to get the required checks
+      - name: Run Build & Test on release PR
+        if: steps.pr.outputs.number
+        env:
+          PR_NUMBER: ${{ steps.pr.outputs.number }}
+          PR_BRANCH: ${{ steps.pr.outputs.branch }}
+        run: |
+          gh workflow run build-test.yml --ref "$PR_BRANCH"
+          sleep 30
+          gh pr checks "$PR_NUMBER" --required --watch --fail-fast --interval 30
+
+      - name: Merge release PR
+        if: steps.pr.outputs.number
+        env:
+          PR_NUMBER: ${{ steps.pr.outputs.number }}
+          PR_SHA: ${{ steps.pr.outputs.sha }}
+        run: gh pr merge "$PR_NUMBER" --squash --match-head-commit "$PR_SHA"
+
+      # The merge push is made with GITHUB_TOKEN and won't start this workflow on its own
+      - name: Trigger release
+        if: steps.pr.outputs.number
+        run: gh workflow run release.yml --ref main
+
   build-and-publish:
     name: Build & Publish