Bump postcss-loader from 5.3.0 to 6.1.0

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 5.3.0 to 6.1.0.
- [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...v6.1.0)

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

package.json

@@ -37,7 +37,7 @@
     "mini-css-extract-plugin": "^1.6.0",
     "node-sass": "^4.14.1",
     "postcss": "^8.3.0",
-    "postcss-loader": "^5.3.0",
+    "postcss-loader": "^6.1.0",
     "postcss-preset-env": "^6.7.0",
     "sass-loader": "^11.1.1",
     "shx": "^0.3.3",