Fix permissions for mypy-primer-comments (#5259)

Based on https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#permissions

Author: JelleZijlstra

.github/workflows/mypy_primer_comment.yml

@@ -10,7 +10,7 @@ on:
 
 permissions:
   contents: read
-  issues: write
+  pull-requests: write
 
 jobs:
   mypy_primer: