[BUG]为什么fastjson2序列化时个别字段首字母变成了大写，但是fastjson却是正常的

### 问题描述
为什么fastjson2序列化时个别字段首字母变成了大写，但是fastjson却是正常的？具体：
Bean Field
Serialize Result

### 环境信息

- OS信息： [e.g.：Mac]
- JDK信息： [e.g.：Openjdk 1.8.0_341]
- 版本信息：[e.g.：Fastjson2 2.0.20]

### 重现步骤
始终重现，JSON.toJSONString(bean)

### 期待的正确结果
期待应该严格按照bean field序列化

### 相关日志输出

#### 附加信息

Start at the JSON.toJSONString(bean) entry point and compare fastjson2's output with fastjson for the bean shown in the attached images. Reproduce the field-name capitalization difference and inspect the serializer's field naming behavior. Done means bean fields retain their expected names in the serialized JSON and the regression is covered by a test.

Written by the indexing model from the issue text.