[Bug Report] el-dialog repeatedly trigger the click event

### Element UI version
2.15.1

### OS/Browsers version
win10/chrome 88.0.4324.190

### Vue version
2.6.12

### Reproduction Link
https://jsfiddle.net/59wju1yv/3/

### Steps to reproduce
通过el-button的click方法打开el-dialog后不关闭dialog的情况下，按下回车键

### What is Expected?
不会触发button的click事件

### What is actually happening?
会触发el-button的click事件（button没有监听回车事件），导致click方法重复调用。