dx: Don't run pkg-pr workflow on PRs from forks (#1024)

Author: mhawryluk

.github/workflows/pkg-pr.yml

@@ -4,6 +4,7 @@ on: [pull_request]
 
 jobs:
   build-and-publish:
+    if: github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     permissions:
       contents: write