Bump black from 21.4b2 to 21.5b0

Bumps [black](https://github.com/psf/black) from 21.4b2 to 21.5b0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/master/CHANGES.md)
- [Commits](https://github.com/psf/black/commits)

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

requirements-lint.txt

@@ -4,5 +4,5 @@ pydocstyle==6.0.0
 pygments
 restructuredtext-lint==1.3.2
 mypy==0.812
-black==21.4b2
+black==21.5b0
 -r requirements-test.txt