fix: handle receiving a list of Message as input for team arun (#4167)

Receiving a list of `Message` as input of `Team.arun` was valid based on
the type signature, but broke when getting the user message

Author: manuhortet

libs/agno/agno/team/team.py

@@ -5645,7 +5645,7 @@ def _get_user_message(
                 if isinstance(message, str):
                     user_message_content = message
                 else:
-                    user_message_content = "\n".join(message)
+                    user_message_content = "\n".join(str(message))
 
             # Add references to user message
             if (