deps(example): bump postcss

Bumps the dependencies group in /examples/nextjs-14-nextauth-4 with 1 update: [postcss](https://github.com/postcss/postcss).


Updates `postcss` from 8.5.0 to 8.5.1
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.0...8.5.1)

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

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