chore(deps): bump postcss and expo

Bumps [postcss](https://github.com/postcss/postcss) to 8.5.15 and updates ancestor dependency [expo](https://github.com/expo/expo/tree/HEAD/packages/expo). These dependencies need to be updated together.


Updates `postcss` from 8.4.49 to 8.5.15
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.49...8.5.15)

Updates `expo` from 54.0.34 to 56.0.12
- [Changelog](https://github.com/expo/expo/blob/main/CHANGELOG.md)
- [Commits](https://github.com/expo/expo/commits/HEAD/packages/expo)

---
updated-dependencies:
- dependency-name: expo
  dependency-version: 56.0.12
  dependency-type: direct:production
- dependency-name: postcss
  dependency-version: 8.5.15
  dependency-type: indirect
...

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

Author: dependabot[bot]