Add permissions to codeowners merge workflow (microsoft#1688)

Author: jakebailey

.github/workflows/codeowners-merge.yml

@@ -4,6 +4,10 @@ on:
   issue_comment: { types: [created] }
   pull_request_review: { types: [submitted] }
 
+permissions:
+  contents: write
+  pull-requests: write
+
 jobs:
   build:
     runs-on: ubuntu-latest