Bump black from 21.6b0 to 21.7b0 (#5320)

Bumps [black](/~https://github.com/psf/black) from 21.6b0 to 21.7b0.
- [Release notes](/~https://github.com/psf/black/releases)
- [Changelog](/~https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](/~https://github.com/psf/black/commits)

---
updated-dependencies:
- dependency-name: black
  dependency-type: direct:development
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Dirk Groeneveld <dirkg@allenai.org>

dev-requirements.txt

@@ -7,7 +7,7 @@ flake8
 mypy==0.910
 
 # Automatic code formatting
-black==21.6b0
+black==21.7b0
 
 # Allows generation of coverage reports with pytest.
 pytest-cov