[Bug Report] Error occurs while preprocessing scss style with dart-sass

### Element UI version
2.15.9

### OS/Browsers version
103.0.5060.114（正式版本） (arm64)

### Vue version
2.6.11

### Reproduction Link
https://codesandbox.io/s/delicate-pine-cu89x0?file=/src/App.vue

### Steps to reproduce
1.使用 dart-sass 作为preprocessor
2.引入 $--breakpoints 变量并使用
3. 报错

### What is Expected?
正常编译

### What is actually happening?
Error， 报错如下：
expected "(".
╷
17 │ @media only screen and "(min-width: 768px) and (max-width: 991px)"{
│ ^
╵
stdin 17:28 res()
stdin 27:7 root stylesheet

Start with the linked CodeSandbox reproduction and inspect how the $--breakpoints variable is processed by the SCSS preprocessor. Reproduce the reported dart-sass error around the generated media query, then verify that the example compiles successfully with dart-sass.

Written by the indexing model from the issue text.