el-scrollbar 的重新计算存在问题

### Description

为el-scrollbar 设置动态高度，滚动条的位置不太正确
![Uploading image.png…]()

### Reproduce Steps

1. [First Step]
2. [Second Step]
3. [and so on...]

### Error Trace (if possible)

It's better to post up the error stack for us to trace this issue.

### Solution

What needs to be done to address this issue? Ideally, provide a pull request with a fix.

### Additional Information

Any additional information, configuration or data that might be necessary to reproduce the issue.