Bump css-loader from 3.3.2 to 3.4.0 (#12673)

Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 3.3.2 to 3.4.0.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/css-loader/compare/v3.3.2...v3.4.0

)

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