build(deps-dev): bump postcss from 8.4.27 to 8.4.31 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.27 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.27...8.4.31)

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

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

frontend/package.json

@@ -49,7 +49,7 @@
     "eslint-plugin-prettier": "^5.0.0",
     "eslint-plugin-vue": "^9.16.1",
     "jsdom": "^22.1.0",
-    "postcss": "^8.4.27",
+    "postcss": "^8.4.31",
     "prettier": "^3.0.1",
     "terser": "^5.19.2",
     "vite": "^4.4.9",