Bump postcss, lux-design-system, postcss-import and vue-loader

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.38 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss), [lux-design-system](https://github.com/pulibrary/lux), [postcss-import](https://github.com/postcss/postcss-import) and [vue-loader](https://github.com/vuejs/vue-loader). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 to 8.4.38
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.39...8.4.38)

Updates `lux-design-system` from 4.4.0 to 5.0.0-beta.6
- [Release notes](https://github.com/pulibrary/lux/releases)
- [Commits](https://github.com/pulibrary/lux/commits)

Updates `postcss-import` from 12.0.1 to 15.1.0
- [Release notes](https://github.com/postcss/postcss-import/releases)
- [Changelog](https://github.com/postcss/postcss-import/blob/master/CHANGELOG.md)
- [Commits](postcss/postcss-import@12.0.1...15.1.0)

Updates `vue-loader` from 15.10.1 to 17.4.2
- [Release notes](https://github.com/vuejs/vue-loader/releases)
- [Changelog](https://github.com/vuejs/vue-loader/blob/main/CHANGELOG.md)
- [Commits](vuejs/vue-loader@v15.10.1...v17.4.2)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: lux-design-system
  dependency-type: direct:production
- dependency-name: postcss-import
  dependency-type: direct:production
- dependency-name: vue-loader
  dependency-type: direct:production
...

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