[Bug Report] 表格固定列，滑动横向滚动出现内容样式显示异常

### Element UI version
2.15.14

### OS/Browsers version
chrome

### Vue version
2.6.12

### Reproduction Link
https://private-user-images.githubusercontent.com/32285384/523624375-5a0fd28e-c84b-46df-859f-728505cebcb0.png?jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.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.LU6VviBrDDmd_zXg0ulBAOBdCx_kNWyhS9Rb5wsyw4U

### Steps to reproduce
表格右侧存在固定列，来回滑动表格横向滚动条和竖向滚动条会出现本该隐藏在固定列下方的内容显示在固定列

### What is Expected?
表格内容显示正常，固定列下方内容不会穿透显示

### What is actually happening?
固定列下方的内容穿透在固定列上方显示了