Replace Mergify with GitHub Actions automerge workflow

.github/workflows/automerge.yml

@@ -0,0 +1,34 @@
+name: Automerge
+on:
+  pull_request_target:
+    types: [opened, synchronize, reopened, review_requested]
+
+permissions:
+  contents: write
+  pull-requests: write
+  packages: read
+
+jobs:
+  renovate-automerge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'renovate[bot]'
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Approve PR if not already approved
+        run: |
+          if [ "$(gh pr view "$PR_URL" --json reviewDecision -q .reviewDecision)" != "APPROVED" ]; then
+            gh pr review --approve "$PR_URL"
+          else
+            echo "PR already approved."
+          fi
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for Renovate PRs
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}