Bump postcss from 8.4.21 to 8.4.23

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.21 to 8.4.23.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.21...8.4.23)

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

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

Author: dependabot[bot]

package-lock.json

@@ -31,7 +31,7 @@
     "css-minimizer-webpack-plugin": "4.2.2",
     "html-minifier": "4.0.0",
     "mini-css-extract-plugin": "2.7.2",
-    "postcss": "8.4.21",
+    "postcss": "8.4.23",
     "postcss-loader": "7.1.0",
     "pug": "3.0.2",
     "sass": "1.58.3",