chore: apply ruff's pyupgrade linter rules to modernize Python code with targeted version (#2419)

api/services/message_service.py

@@ -1,5 +1,5 @@
 import json
-from typing import List, Optional, Union
+from typing import Optional, Union
 
 from core.generator.llm_generator import LLMGenerator
 from core.memory.token_buffer_memory import TokenBufferMemory
@@ -177,7 +177,7 @@ class MessageService:
 
     @classmethod
     def get_suggested_questions_after_answer(cls, app_model: App, user: Optional[Union[Account, EndUser]],
-                                             message_id: str, check_enabled: bool = True) -> List[Message]:
+                                             message_id: str, check_enabled: bool = True) -> list[Message]:
         if not user:
             raise ValueError('user cannot be None')