Explicitly allow unsafe pr checkout for LB

Author: liamdugan

.github/workflows/leaderboard-submission.yml

@@ -35,6 +35,7 @@ jobs:
           path: _pr_submission
           repository: ${{ github.event.pull_request.head.repo.full_name }}
           ref: ${{ github.head_ref }}
+          allow-unsafe-pr-checkout: true
 
       # copy submission files over to main repo
       - name: Copy submission files to eval workspace