build(deps-dev): bump postcss from 8.5.5 to 8.5.6 in /frontend

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.6
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

frontend/package-lock.json

@@ -69,7 +69,7 @@
     "knip": "^5.61.0",
     "msw": "^2.10.2",
     "msw-storybook-addon": "^2.0.5",
-    "postcss": "^8.5.5",
+    "postcss": "^8.5.6",
     "postcss-import": "^16.1.1",
     "postcss-nesting": "^13.0.2",
     "rimraf": "^6.0.1",