chore(deps): bump postcss, @storybook/react and css-loader

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss), [@storybook/react](https://github.com/storybookjs/storybook/tree/HEAD/code/renderers/react) and [css-loader](https://github.com/webpack-contrib/css-loader). These dependencies need to be updated together.


Updates `postcss` from 6.0.23 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@6.0.23...8.4.31)

Updates `@storybook/react` from 4.1.18 to 7.4.6
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/next/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v7.4.6/code/renderers/react)

Updates `css-loader` from 2.1.1 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@v2.1.1...v6.8.1)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: "@storybook/react"
  dependency-type: direct:development
- dependency-name: css-loader
  dependency-type: direct:development
...

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