[Bug Report] Search-select pop up the drop-down option automatically when I switch back to the page.

### Element UI version
2.15.7

### OS/Browsers version
window 10 / Chrome 96.0.4664.110

### Vue version
2.6.14

### Reproduction Link
https://codesandbox.io/s/lively-waterfall-ojsud?file=/src/App.vue

### Steps to reproduce
1. select one of drop-down option. （选择下拉框选项中的任意一项）
2. switch to other page.（切换到其他页面）
3. switch back to the page.（切换回原来select的页面）
4. you can find search-select pop up the drop-down option automatically.（你会发现组件自动弹出下拉项内容）

### What is Expected?
I hope that when I click SELECT that pop up the pull box instead of moving.
（我希望当我点击 select 的时候，才弹出下拉框，而不是自动弹出。）

### What is actually happening?
After switching to other pages, switch back, the Select drop-down item is automatically popped up.
（切换到其他页面后，再切换回来，select 下拉项自动弹出。）