build(deps-dev): bump postcss from 8.4.39 to 8.4.40 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.39 to 8.4.40.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.39...8.4.40)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

frontend/package-lock.json

@@ -74,7 +74,7 @@
     "eslint-plugin-matrix-org": "^1.2.1",
     "happy-dom": "^14.12.3",
     "i18next-parser": "^9.0.1",
-    "postcss": "^8.4.39",
+    "postcss": "^8.4.40",
     "postcss-modules": "^6.0.0",
     "postcss-nesting": "^12.1.5",
     "prettier": "3.3.2",