Bump postcss from 8.3.0 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.0 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.3.0...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

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

package.json

@@ -23,7 +23,7 @@
     "core-js": "^3.6.5",
     "finalhandler": "^1.1.2",
     "mdn-polyfills": "^5.20.0",
-    "postcss": "^8.2.10",
+    "postcss": "^8.4.31",
     "postcss-css-variables": "^0.17.0",
     "postcss-flexbugs-fixes": "^4.2.1",
     "postcss-import": "^12.0.1",