The check box in [bug report] tree triggers async validator, causing an exception to be thrown when calling resetfields()

### Element UI version
2.14.1

### OS/Browsers version
Windows 10

### Vue version
2.6.12

### Reproduction Link
https://github.com/ElemeFE/element/issues/new/choose

### Steps to reproduce
封装一个 TreeSelect，需要与 FormItem 联动校验，现在在 resetFields 事件中触发了 Tree 中 Checkbox 组件，而 Checkbox 的 change 事件又触发了校验，引发了异常。

### What is Expected?
Tree 中 Checkbox 组件点击不触发 validator

### What is actually happening?
Tree 中 Checkbox 组件点击触发了 validator