feat: unblock community contributions in PR reviews (#115)

Restricts the automatic PR review workflow to run only for pull requests
opened by repository owners, members, or collaborators. This is a
temporary fix for requiring env vars in forks.

Author: jerop

.github/workflows/gemini-pr-review.yml

@@ -36,7 +36,13 @@ jobs:
   review-pr:
     if: |-
       github.event_name == 'workflow_dispatch' ||
-      (github.event_name == 'pull_request' && github.event.action == 'opened') ||
+      (github.event_name == 'pull_request' && github.event.action == 'opened' &&
+        (
+          github.event.pull_request.author_association == 'OWNER' ||
+          github.event.pull_request.author_association == 'MEMBER' ||
+          github.event.pull_request.author_association == 'COLLABORATOR'
+        )
+      ) ||
       (github.event_name == 'issue_comment' && github.event.issue.pull_request &&
         contains(github.event.comment.body, '@gemini-cli /review') &&
         (