Bump postcss-loader from 6.2.1 to 7.0.0 (#868)

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 6.2.1 to 7.0.0.
- [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@v6.2.1...v7.0.0)

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

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

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

package.json

@@ -40,7 +40,7 @@
 		"mini-css-extract-plugin": "^2.6.0",
 		"npm-run-all": "^4.1.5",
 		"postcss": "^8.4.14",
-		"postcss-loader": "^6.2.1",
+		"postcss-loader": "^7.0.0",
 		"postcss-preset-env": "^7.5.0",
 		"prettier": "npm:wp-prettier@^2.6.2-beta-1",
 		"sass-loader": "^12.6.0",