chore(release): add pull-requests: write permission to on_issue_comment workflow (bazel-contrib#3893)

Update on_issue_comment.yaml to request pull-requests: write permission,
which is required for release_prepare.yaml.

Author: rickeylev

.github/workflows/on_issue_comment.yaml

@@ -7,6 +7,7 @@ on:
 permissions:
   contents: write
   issues: write
+  pull-requests: write
 
 jobs:
   # This job always runs to prevent GHA from marking the run as failed when