remove checkout ref on cleanup

Author: shortcuts

.github/workflows/codegen-cleanup.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0
-          ref: ${{ github.event.pull_request.head.ref }}
+          ref: main
 
       - name: Setup
         id: setup