Disable the automerge Action for repo-sync (#18711)

Instead, rely on the official GitHub auto-merge feature

Author: JamesMGreene

.github/workflows/repo-sync.yml

@@ -115,7 +115,7 @@ jobs:
           destination_branch: main
           pr_title: 'repo sync'
           pr_body: "This is an automated pull request to sync changes between the public and private repos.\n\n:robot: This pull request should be merged (not squashed) to preserve continuity across repos, so please let a bot do the merging!"
-          pr_label: automerge,autoupdate,automated-reposync-pr
+          pr_label: autoupdate,automated-reposync-pr
           github_token: ${{ secrets.OCTOMERGER_PAT_WITH_REPO_AND_WORKFLOW_SCOPE }}
 
       - name: Find pull request