.github/workflows: Update pull-request workflow for permissions quirk

Reference: https://github.com/CodelyTV/pr-size-labeler/blob/b1ba00967bee9f8d557e89615ae75626e26f004e/src/github.sh#L55
Reference: https://docs.github.com/en/rest/overview/permissions-required-for-github-apps#permission-on-pull-requests

Author: bflad

.github/workflows/pull-request.yml

@@ -3,6 +3,8 @@ name: "Pull Request Triage"
 on: [pull_request_target]
 
 permissions:
+  # CodelyTV/pr-size-labeler uses issues URL for labeling
+  issues: write
   pull-requests: write
 
 jobs: