Make lint CI show diff

Author: zliang-akamai

.github/workflows/ci.yml

@@ -67,7 +67,7 @@ jobs:
           gofumpt -l -w .
 
       - name: Fail if changes
-        run: git diff-index --exit-code HEAD
+        run: git diff --exit-code HEAD
 
   test:
     runs-on: ubuntu-latest