fix wrong type

lightrag/base.py

@@ -69,7 +69,7 @@ class QueryParam:
     ll_keywords: list[str] = field(default_factory=list)
     """List of low-level keywords to refine retrieval focus."""
 
-    conversation_history: list[dict[str, Any]] = field(default_factory=list)
+    conversation_history: list[dict[str, str]] = field(default_factory=list)
     """Stores past conversation history to maintain context.
     Format: [{"role": "user/assistant", "content": "message"}].
     """