⬆️ Bump black from 20.8b1 to 21.9b0

Bumps [black](https://github.com/psf/black) from 20.8b1 to 21.9b0.
- [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>

pyproject.toml

@@ -26,7 +26,7 @@ pandas = "^1.0.1"
 pre-commit = "^2.8.2"
 pyupgrade = "^2.7.3"
 isort = "^5.6.4"
-black = "^20.8b1"
+black = "^21.9b0"
 mypy = "^0.790"
 bandit = "^1.6.2"
 safety = "^1.9.0"