added missing type

lightrag/operate.py

@@ -573,7 +573,7 @@ async def kg_query(
     global_config: dict[str, str],
     hashing_kv: BaseKVStorage | None = None,
     system_prompt: str | None = None,
-) -> str:
+) -> str | AsyncIterator[str]:
     # Handle cache
     use_model_func = global_config["llm_model_func"]
     args_hash = compute_args_hash(query_param.mode, query, cache_type="query")