feat: simplify auto merge workflow

.github/workflows/dependabot.auto.yml

@@ -4,24 +4,13 @@ on:
   pull_request:
 
 jobs:
-  worker:
+  dependabot:
+    name: 'Dependabot'
     runs-on: ubuntu-latest
-
-    if: github.actor == 'dependabot[bot]'
+    if: ${{ github.actor == 'dependabot[bot]' && github.event_name == 'pull_request'}}
     steps:
-      - name: automerge
-        uses: actions/github-script@0.2.0
-        with:
-          script: |
-            github.pullRequests.createReview({
-              owner: context.payload.repository.owner.login,
-              repo: context.payload.repository.name,
-              pull_number: context.payload.pull_request.number,
-              event: 'APPROVE'
-            })
-            github.pullRequests.merge({
-              owner: context.payload.repository.owner.login,
-              repo: context.payload.repository.name,
-              pull_number: context.payload.pull_request.number
-            })
-          github-token: ${{github.token}}
+      - name: Enable auto-merge for Dependabot PRs
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: ${{secrets.TOKEN_GITHUB}}