Update automerge.yml (#263)

Author: jeswr

.github/workflows/automerge.yml

@@ -11,6 +11,7 @@ jobs:
       contents: write
       pull-requests: write
       repository-projects: write
+    if: github.actor == 'dependabot[bot]'
     steps:
       - uses: actions/checkout@v4
       - run: gh pr merge ${{ github.event.pull_request.html_url }} --auto --squash