Fix Greetings workflow permissions

Add issues: write and pull-requests: write permissions required
for the reusable workflow to post welcome comments.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: clubanderson

.github/workflows/greetings.yml

@@ -8,6 +8,8 @@ on:
 
 permissions:
   contents: read
+  issues: write
+  pull-requests: write
 
 jobs:
   greet: