Bump yaml and postcss-loader in /static (#57)

Removes [yaml](https://github.com/eemeli/yaml). It's no longer used after updating ancestor dependency [postcss-loader](https://github.com/webpack-contrib/postcss-loader). These dependencies need to be updated together.


Removes `yaml`

Updates `postcss-loader` from 7.0.1 to 7.2.4
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/postcss-loader@v7.0.1...v7.2.4)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>