fix: correct variable references in chat message constructor

Author: lss233

framework/workflow/implementations/blocks/llm/chat.py

@@ -63,11 +63,11 @@ def execute(self, user_msg: IMMessage, memory_content: str, system_prompt_format
         executor = self.container.resolve(WorkflowExecutor)
 
         # 先替换自有的两个变量
-        system_prompt_format = self.system_prompt_format.replace("{user_msg}", user_msg.content)
+        system_prompt_format = system_prompt_format.replace("{user_msg}", user_msg.content)
         system_prompt_format = system_prompt_format.replace("{user_name}", user_msg.sender.display_name)
         system_prompt_format = system_prompt_format.replace("{memory_content}", memory_content)
 
-        user_prompt_format = self.user_prompt_format.replace("{user_msg}", user_msg.content)
+        user_prompt_format = user_prompt_format.replace("{user_msg}", user_msg.content)
         user_prompt_format = user_prompt_format.replace("{user_name}", user_msg.sender.display_name)
         user_prompt_format = user_prompt_format.replace("{memory_content}", memory_content)