⬆️ Bump postcss from 8.4.22 to 8.4.31 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.22 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/8.4.22...8.4.31)

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

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

frontend/package.json

@@ -77,7 +77,7 @@
 		"minisearch": "^6.0.1",
 		"pikaso": "^2.7.6",
 		"plausible-tracker": "^0.3.8",
-		"postcss": "^8.4.22",
+		"postcss": "^8.4.31",
 		"postcss-import": "^15.1.0",
 		"postcss-load-config": "^4.0.1",
 		"prettier": "^2.8.8",