chore(proxy): mark the unused os.walk dirs name in the UI rewrite helper

Moving the loop into _apply_server_root_path_to_ui made dirs a function
local, which basedpyright reports as reportUnusedVariable.

litellm/proxy/proxy_server.py

@@ -2380,7 +2380,7 @@ try:
         )
 
     def _apply_server_root_path_to_ui(ui_dir: str, server_root_path: str) -> None:
-        for root, dirs, files in os.walk(ui_dir):
+        for root, _dirs, files in os.walk(ui_dir):
             for filename in files:
                 file_path = os.path.join(root, filename)
                 # Skip binary files and files that don't need path replacement