Auto merge patch Dependabot PRs

We currently merge all Dependabot PRs manually.

This commit introduces a GitHub Action to automatically merge `patch`
Dependabot PRs.

Ref:
- https://semver.org/
- https://github.com/ahmadnassri/action-dependabot-auto-merge

.github/workflows/auto-merge.yml

@@ -0,0 +1,15 @@
+---
+name: auto-merge
+
+on:
+  pull_request:
+
+jobs:
+  auto-merge:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ahmadnassri/action-dependabot-auto-merge@v2
+        with:
+          target: patch
+          github-token: ${{ secrets.AUTO_MERGE_GITHUB_ACCESS_TOKEN }}