Bump postcss and next in /apps/custom-ui-floating-window-demo

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [next](https://github.com/vercel/next.js). These dependencies need to be updated together.


Updates `postcss` from 8.4.14 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@8.4.14...8.4.31)

Updates `next` from 13.0.5 to 13.5.4
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v13.0.5...v13.5.4)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: next
  dependency-type: direct:production
...

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

Author: dependabot[bot]

apps/custom-ui-floating-window-demo/package-lock.json

@@ -14,7 +14,7 @@
     "bootstrap": "^5.2.3",
     "cookies-next": "^2.1.1",
     "eslint-config-next": "13.0.5",
-    "next": "13.0.5",
+    "next": "13.5.4",
     "pino": "^8.7.0",
     "pino-pretty": "^9.1.1",
     "pipedrive": "^17.5.4",