[Bug Report] Use tree Data in Table - when you use the toggleRowSelection to set a leaf row checked，it didn't worked

### Element UI version
2.13.2

### OS/Browsers version
window 10/chrome 86

### Vue version
3.0.0-beta.15

### Reproduction Link
https://codepen.io/luo7023539/pen/MWKmpNB?editors=1111

### Steps to reproduce
使用toggleRowSelection设置某个子节点选中

### What is Expected?
子节点被选中

### What is actually happening?
不生效