🧐[问题] ProTable 表头分组后，无法正常搜索

### 🧐 问题描述
在使用表头分组的情况下，无法搜索子表头的字段


### 💻 示例代码

```
import { ProTable } from '@ant-design/pro-table';

const columns = [
{
title: '基本信息',
children: [
{
title: '姓名',
dataIndex: 'name',
key: 'name',
},
{
title: '年龄',
dataIndex: 'age',
key: 'age',
},
],
},
{
title: '联系信息',
children: [
{
title: '邮箱',
dataIndex: 'email',
key: 'email',
},
{
title: '电话',
dataIndex: 'phone',
key: 'phone',
},
],
},
];
```

Start at ProTable's search handling and reproduce the issue with the grouped columns shown in the report. Verify that the child fields name, age, email, and phone can be searched when their columns are nested under grouped headers.

Written by the indexing model from the issue text.