Bump postcss from 8.5.6 to 8.5.12 in /server/frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.6 to 8.5.12.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.6...8.5.12)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.12
  dependency-type: direct:development
...

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

Author: dependabot[bot]

server/frontend/package-lock.json

@@ -44,7 +44,7 @@
     "jest-environment-jsdom": "^29.7.0",
     "jest-transform-stub": "^2.0.0",
     "mini-css-extract-plugin": "^1.6.0",
-    "postcss": "^8.3.5",
+    "postcss": "^8.5.12",
     "prettier": "^3.3.2",
     "vue-loader": "^17.4.2",
     "webpack": "^5.94.0",