build(deps-dev): bump blacken-docs from 1.19.0 to 1.19.1 (#578)

Bumps [blacken-docs](https://github.com/asottile/blacken-docs) from 1.19.0 to 1.19.1.
- [Changelog](https://github.com/adamchainz/blacken-docs/blob/main/CHANGELOG.rst)
- [Commits](adamchainz/blacken-docs@1.19.0...1.19.1)

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

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