Bump postcss-loader from 5.3.0 to 6.2.1

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 5.3.0 to 6.2.1.
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/postcss-loader/compare/v5.3.0...v6.2.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -51,7 +51,7 @@
     "mini-css-extract-plugin": "^1.4.0",
     "node-sass": "^6.0.0",
     "postcss": "^8.2.7",
-    "postcss-loader": "^5.2.0",
+    "postcss-loader": "^6.2.1",
     "sass": "^1.32.8",
     "sass-loader": "^11.0.1",
     "style-loader": "^2.0.0",