build(deps-dev): bump postcss-loader from 4.0.3 to 4.0.4

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 4.0.3 to 4.0.4.
- [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@v4.0.3...v4.0.4)

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

unison-ui/package.json

@@ -48,7 +48,7 @@
     "plugin-error": "^1.0.1",
     "postcss-font-magician": "^2.3.1",
     "postcss-import": "^12.0.1",
-    "postcss-loader": "^4.0.3",
+    "postcss-loader": "^4.0.4",
     "postcss-mixins": "^6.2.3",
     "postcss-nested": "^4.2.3",
     "postcss-preset-env": "^6.3.0",