Refactor feedback section in chapter 4

Removed code block formatting from last code attempt section.

docs/chapter4/第四章 智能体经典范式构建.md

@@ -1023,9 +1023,7 @@ REFINE_PROMPT_TEMPLATE = """
 {task}
 
 # 你上一轮尝试的代码:
-```python
 {last_code_attempt}
-```
 评审员的反馈：
 {feedback}