After the [bug report] table structure uses show overflow tooltip, the total line has no such effect

### Element UI version
2.15.6

### OS/Browsers version
Windows10/Google Chrome 90.0

### Vue version
2.6.14

### Reproduction Link
https://codepen.io/jiangguangyao/pen/LYLjmKg

### Steps to reproduce
看数值1那一列，设置show-overflow-tooltip后，第四行可正常显示溢出裁切省略号 tooltip，但合计行的数据没变

### What is Expected?
数值1这一列的合计行也展示出show-overflow-tooltip的效果

### What is actually happening?
数值1这一列的合计行未展示溢出裁切效果