Bump postcss and css-loader

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [css-loader](https://github.com/webpack-contrib/css-loader). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.39...8.4.31)

Updates `css-loader` from 3.6.0 to 6.8.1
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/css-loader@v3.6.0...v6.8.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -25,7 +25,7 @@
     "babel-jest": "^25.4.0",
     "babel-loader": "^9.1.0",
     "clean-webpack-plugin": "^3.0.0",
-    "css-loader": "^3.6.0",
+    "css-loader": "^6.8.1",
     "file-loader": "^6.2.0",
     "jest": "^28.1.3",
     "jest-environment-jsdom": "^28.1.3",