Enable auto-merge for dependabot (nginx#5801)

Author: oseoin

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

@@ -0,0 +1,23 @@
+name: Dependabot auto-merge
+on: pull_request_target
+
+permissions:
+  contents: read
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-22.04
+    if: ${{ github.event.pull_request.user.login == 'dependabot[bot]' }}
+    permissions:
+      pull-requests: write
+      contents: write
+    steps:
+      - name: Dependabot metadata
+        id: dependabot-metadata
+        uses: dependabot/fetch-metadata@5e5f99653a5b510e8555840e80cbf1514ad4af38 # v2.1.0
+
+      - name: Enable auto-merge for Dependabot PRs
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: ${{ secrets.NGINX_PAT }}