build(deps-dev): bump mkdocstrings from 0.21.1 to 0.21.2 (#644)

Bumps [mkdocstrings](https://github.com/mkdocstrings/mkdocstrings) from 0.21.1 to 0.21.2.
- [Release notes](https://github.com/mkdocstrings/mkdocstrings/releases)
- [Changelog](https://github.com/mkdocstrings/mkdocstrings/blob/master/CHANGELOG.md)
- [Commits](mkdocstrings/mkdocstrings@0.21.1...0.21.2)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>