build(deps): bump rehype-slug from 5.1.0 to 6.0.0

Bumps [rehype-slug](https://github.com/rehypejs/rehype-slug) from 5.1.0 to 6.0.0.
- [Release notes](https://github.com/rehypejs/rehype-slug/releases)
- [Commits](rehypejs/rehype-slug@5.1.0...6.0.0)

---
updated-dependencies:
- dependency-name: rehype-slug
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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