Bump markdownz from 8.3.2 to 8.4.0

Bumps [markdownz](https://github.com/zooniverse/markdownz) from 8.3.2 to 8.4.0.
- [Release notes](https://github.com/zooniverse/markdownz/releases)
- [Changelog](https://github.com/zooniverse/markdownz/blob/master/CHANGELOG.md)
- [Commits](zooniverse/markdownz@v8.3.2...v8.4.0)

---
updated-dependencies:
- dependency-name: markdownz
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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