[Bug Report] autocomplete : the interaction selected up by the keyboard is not consistent

### Element UI version
2.15.1

### OS/Browsers version
macOS Big Sur 11.2.3 /chrome 版本 89.0.4389.114（正式版本） (x86_64)

### Vue version
2.6.12

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

### Steps to reproduce
When the keyboard selects down to the bottom of the scroll bar, and then selects up to the last visible element, it will scroll down the height of an element to display the previous element. However, if the keyboard does not select the bottom down, it will not scroll down the height of an element to display the previous element. Is the judgment of offsettop < scrolltop in the highlight method of the source code inaccurate?

### What is Expected?
The interaction between the two is consistent？

### What is actually happening?
The interaction between the two is not consistent