Build(deps-dev): Bump postcss from 8.4.38 to 8.4.39 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.38 to 8.4.39.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.38...8.4.39)

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

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

frontend/package.json

@@ -28,7 +28,7 @@
     "html-webpack-plugin": "^5.6.0",
     "jest": "^27.5.1",
     "mini-css-extract-plugin": "^2.9.0",
-    "postcss": "^8.4.38",
+    "postcss": "^8.4.39",
     "postcss-loader": "^8.1.1",
     "prettier": "^3.3.2",
     "prop-types": "^15.8.1",