chore(deps): bump postcss, css-loader and vue-loader

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss), [css-loader](https://github.com/webpack-contrib/css-loader) and [vue-loader](https://github.com/vuejs/vue-loader). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.39...8.4.31)

Updates `css-loader` from 3.5.3 to 6.8.1
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/css-loader@v3.5.3...v6.8.1)

Updates `vue-loader` from 15.9.2 to 17.2.2
- [Release notes](https://github.com/vuejs/vue-loader/releases)
- [Changelog](https://github.com/vuejs/vue-loader/blob/main/CHANGELOG.md)
- [Commits](vuejs/vue-loader@v15.9.2...v17.2.2)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: css-loader
  dependency-type: direct:development
- dependency-name: vue-loader
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>