fix:python Invert condition for merge_state deprecation check (CopilotKit#1749)

Author: nickstanish

sdk-python/copilotkit/langgraph_agent.py

@@ -157,7 +157,7 @@ def __init__(
         if agent is not None:
             logger.warning("Warning: agent is deprecated, use graph instead")
 
-        if merge_state is None:
+        if merge_state is not None:
             logger.warning("Warning: merge_state is deprecated, use copilotkit_config instead")
 
         if graph is None and agent is None: