Use GitHub Action for Dependabot (#314)

.github/workflows/dependabot.yaml

@@ -0,0 +1,13 @@
+name: dependabot
+on: pull_request
+permissions:
+  contents: write
+  pull-requests: write
+jobs:
+  merge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - run: gh pr merge --auto --squash ${{ github.event.pull_request.html_url }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}