permissions, update head ref

Signed-off-by: Jason Hall <jason@chainguard.dev>

.github/workflows/codegen.yaml

@@ -4,12 +4,19 @@ on:
   pull_request:
     branches: [main]
 
+permissions: {}
+
 jobs:
   build:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
 
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
+          token: ${{ secrets.GITHUB_TOKEN }}
       - uses: actions/setup-go@v5
       - run: |
           sudo apt-get update