Don't make git diff quiet

Also only check the redcode directory.

Author: ian-h-chamberlain

.github/workflows/redcode-ci.yml

@@ -28,4 +28,4 @@ jobs:
     - name: Build extension
       run: npm run build
     - name: Verify the build did not modify any files
-      run: git diff-index --quiet HEAD
+      run: git diff-index HEAD -- .