Delete pre-commit auto-update branch when pull request is closed

Author: zachborboa

.github/workflows/pre-commit-auto-update.yml

@@ -44,6 +44,7 @@ jobs:
             ```
           author: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
           committer: GitHub <noreply@github.com>
+          delete-branch: true
 
       - name: Pull request created
         if: ${{ steps.cpr.outputs.pull-request-number }}