Bump postcss, autoprefixer and css-loader

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.32 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss), [autoprefixer](https://github.com/postcss/autoprefixer) and [css-loader](https://github.com/webpack-contrib/css-loader). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 to 8.4.32
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.39...8.4.32)

Updates `autoprefixer` from 9.8.0 to 10.4.16
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](postcss/autoprefixer@9.8.0...10.4.16)

Updates `css-loader` from 3.6.0 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@v3.6.0...v6.8.1)

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

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