The "remote search" component icon of the [bug report] select component cannot be displayed normally

### Element UI version
2.15.5

### OS/Browsers version
macOS11.5.2 / Chrome 95.0.4638.69

### Vue version
2.6.11

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

### Steps to reproduce
官方文档demo即可复现，原因可能是“远程搜索”的icon类名为el-select__caret el-input__icon el-icon- ， 而其他用法的类名为el-select__caret el-input__icon el-icon-arrow-up

### What is Expected?
icon正常显示

### What is actually happening?
icon无法正常显示