Bump yaml and astro in /demo

Removes [yaml](https://github.com/eemeli/yaml). It's no longer used after updating ancestor dependency [astro](https://github.com/withastro/astro/tree/HEAD/packages/astro). These dependencies need to be updated together.


Removes `yaml`

Updates `astro` from 1.5.2 to 2.3.0
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/astro/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/astro@2.3.0/packages/astro)

---
updated-dependencies:
- dependency-name: yaml
  dependency-type: indirect
- dependency-name: astro
  dependency-type: direct:development
...

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

Author: dependabot[bot]