Bump schemars from 0.8.19 to 0.8.21

Bumps [schemars](https://github.com/GREsau/schemars) from 0.8.19 to 0.8.21.
- [Release notes](https://github.com/GREsau/schemars/releases)
- [Changelog](https://github.com/GREsau/schemars/blob/master/CHANGELOG.md)
- [Commits](GREsau/schemars@v0.8.19...v0.8.21)

---
updated-dependencies:
- dependency-name: schemars
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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