ci(dependabot): auto-merge Dependabot PRs once CI passes

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,25 @@
+name: Dependabot auto-merge
+
+on:
+  pull_request:
+    branches: [main]
+    types: [opened, synchronize, reopened, ready_for_review]
+
+# Least privilege: only what enabling auto-merge requires.
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  auto-merge:
+    name: Enable auto-merge
+    runs-on: ubuntu-latest
+    # Only Dependabot PRs. GitHub will hold the merge until the
+    # "Build & Test" required status check on the PR_only ruleset passes.
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    steps:
+      - name: Enable auto-merge (squash)
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}