Enable use-auto-merge for dependency updates

Author: tjenkinson

.github/workflows/automerge.yml

@@ -10,5 +10,5 @@ jobs:
     steps:
       - uses: tjenkinson/gh-action-auto-merge-dependency-updates@v1
         with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
-          allowed-actors: dependabot-preview[bot], dependabot[bot], tjenkinson
+          use-auto-merge: true
+          allowed-actors: dependabot[bot], tjenkinson