Update release-prepare-monthly.yml

Author: mtrezza

.github/workflows/release-prepare-monthly.yml

@@ -41,3 +41,16 @@ jobs:
             
             > [!WARNING]
             > Only use `Merge Commit` to merge this pull request. Do not use `Rebase and Merge` or `Squash and Merge`.
+  auto-merge-pr:
+    needs: create-release-pr
+    runs-on: ubuntu-latest
+    steps:
+      - name: Wait for CI checks to pass
+        uses: hmarr/auto-approve-action@v4
+        with:
+          github-token: ${{ secrets.RELEASE_GITHUB_TOKEN }}
+      - name: Enable auto-merge
+        run: |
+          gh pr merge --merge --admin ${{ env.BRANCH_NAME }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.RELEASE_GITHUB_TOKEN }}