[Bug Report] select组件异步设置disabled，异步设置v-model时会自动设置input的高度为40px

### Element UI version
2.15.6

### OS/Browsers version
windows

### Vue version
2.6.14

### Reproduction Link
https://jsfiddle.net/sfu3avh6/2/

### Steps to reproduce
重现代码
```

错误的input高度，input的高度被强制设置为40px

---

export default {
data () {
return {
testSelect: '',
testSelectOptions: [],
testSelectDisabled: false
}
},
mounted () {
setTimeout(() => {
this.testSelectDisabled = true
this.testSelectOptions = [
{ label: 'Html', value: 'html' },
{ label: 'Javascript', value: 'javascript' },
{ label: 'Css', value: 'css' }
]
this.testSelect = 'javascript'
})
}
}
<scirpt>
```

### What is Expected?
当异步设置select组件的disabled，异步设置v-model时不会自动设置input的高度为40px

### What is actually happening?
当异步设置select组件的disabled，异步设置v-model时input的高度被强制设置为40px

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