Add automerge workflow for Dependabot PRs

Author: koppor

.github/workflows/automerge.yml

@@ -0,0 +1,21 @@
+name: automerge
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  github-actions:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+        with:
+          show-progress: ''
+      - name: Merge PR
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}