Fix prow-action workflow permissions for issue commands

The /assign, /close, /reopen, and other prow commands were failing with
"Resource not accessible by integration" because the workflow's GITHUB_TOKEN
lacked write permissions for issues and pull requests.

Add explicit permissions block to grant the minimum required access.

Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>

Author: shubham-pampattiwar

.github/workflows/prow-action.yml

@@ -5,6 +5,10 @@ on:
   issue_comment:
     types: [created]
 
+permissions:
+  issues: write
+  pull-requests: write
+
 jobs:
   execute:
     runs-on: ubuntu-latest