[Bug]: experiments.css introduces wrong path `\` under Windows when using `publicPath: 'auto'`

### System Info

@rspack/core 1.2.2

### Details

## actual behavior

dist/static/css/index.css 
`background: url(..\../static/svg/logo.svg)`

## expected behavior

dist/static/css/index.css 
`background: url(../../static/svg/logo.svg)`


### Reproduce link

https://github.com/SoonIter/rspack-css-extract-wrong-path/tree/css-experiments

### Reproduce Steps

1. pnpm i
2. npm run build


