Use GITHUB_TOKEN for Dependabot auto merge (#514)

Author: pdabelf5

.github/workflows/dependabot-auto-merge.yml

@@ -20,4 +20,4 @@ jobs:
         run: gh pr merge --auto --squash "$PR_URL"
         env:
           PR_URL: ${{ github.event.pull_request.html_url }}
-          GITHUB_TOKEN: ${{ secrets.NGINX_PAT }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}