fix(ci): comments also appearing on internal prs (#32538)

.github/workflows/external-pr-comment.yml

@@ -10,7 +10,7 @@ permissions:
 jobs:
   comment-on-external-pr:
     runs-on: ubuntu-latest
-    if: github.event.pull_request.repository.full_name != github.repository
+    if: github.event.pull_request.head.repo.full_name != github.repository
     steps:
       - name: Comment on PR
         uses: actions/github-script@v7