fix(lightrag): use is_closed() instead of _closed

lightrag/lightrag.py

@@ -68,7 +68,7 @@ def always_get_an_event_loop() -> asyncio.AbstractEventLoop:
     try:
         # Try to get the current event loop
         current_loop = asyncio.get_event_loop()
-        if current_loop._closed:
+        if current_loop.is_closed():
             raise RuntimeError("Event loop is closed.")
         return current_loop