Bump postcss, tailwindcss and laravel-mix

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss), [tailwindcss](https://github.com/tailwindlabs/tailwindcss) and [laravel-mix](https://github.com/JeffreyWay/laravel-mix). These dependencies need to be updated together.


Updates `postcss` from 5.2.18 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/commits/8.4.31)

Updates `tailwindcss` from 0.7.4 to 3.3.3
- [Release notes](https://github.com/tailwindlabs/tailwindcss/releases)
- [Changelog](https://github.com/tailwindlabs/tailwindcss/blob/master/CHANGELOG.md)
- [Commits](tailwindlabs/tailwindcss@v0.7.4...v3.3.3)

Updates `laravel-mix` from 2.1.14 to 6.0.49
- [Release notes](https://github.com/JeffreyWay/laravel-mix/releases)
- [Changelog](https://github.com/laravel-mix/laravel-mix/blob/master/CHANGELOG.md)
- [Upgrade guide](https://github.com/laravel-mix/laravel-mix/blob/master/UPGRADE.md)
- [Commits](https://github.com/JeffreyWay/laravel-mix/commits)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: tailwindcss
  dependency-type: direct:production
- dependency-name: laravel-mix
  dependency-type: direct:development
...

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