modified workflow for forks

Author: Meghan Krishna Gonugunta

.github/workflows/preview.yml

@@ -9,7 +9,9 @@ permissions:
 
 jobs:
   preview:
+    if: github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
+
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4