Avoid running exception lint twice if PRs originate from the origin repo

.github/workflows/exceptions.yml

@@ -11,6 +11,7 @@ on:
 jobs:
   lint:
     runs-on: ubuntu-latest
+    if: (github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository)
     steps:
       - uses: actions/checkout@v4