build(deps-dev): bump postcss-loader from 7.3.3 to 7.3.4 (destinygg#394)

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.3.3 to 7.3.4.
- [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@v7.3.3...v7.3.4)

---
updated-dependencies:
- dependency-name: postcss-loader
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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