Selecting a table row in the [bug report] El dialog will trigger form validation at the upper level

### Element UI version
2.15.1

### OS/Browsers version
89

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/xiaodun/pen/eYgEzYQ

### Steps to reproduce
1.点击新增显示对话框
2.选中表格中的一行
3.外层的表单验证被触发了

### What is Expected?
选中对话框中表格里的一行，不触发外层的表单验证

### What is actually happening?
选中对话框中表格里的一行，触发了外层的表单验证