[Bug Report] el-date-picker 日期组件选择月份时,默认选中月份样式未清除

[CPenguo]

Element UI version

2.15.7

OS/Browsers version

windows10/chrome 90.0.4430.93

Vue version

2.7.7

Reproduction Link

https://codepen.io/ziyoung/pen/LKNBqB

Steps to reproduce

https://element.eleme.cn/#/zh-CN/component/date-picker

What is Expected?

https://element.eleme.cn/#/zh-CN/component/date-picker

What is actually happening?

https://element.eleme.cn/#/zh-CN/component/date-picker

[CPenguo]