chore: add comment for namespaced filenode

Author: samsonasik

utils/src/Rector/UnderscoreToCamelCaseVariableNameRector.php

@@ -86,6 +86,7 @@ public function getNodeTypes(): array
     public function refactor(Node $node): ?Node
     {
         if ($node instanceof FileNode && $node->isNamespaced()) {
+            // handled in Namespace_ node
             return null;
         }