build(deps): bump black from 21.8b0 to 21.9b0

Bumps [black](https://github.com/psf/black) from 21.8b0 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:production
...

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

pyproject.toml

@@ -10,7 +10,7 @@ python = "^3.8"
 appdirs = "1.4.4"
 attrs = "21.2.0"
 beautifulsoup4 = "4.10.0"
-black = "21.8b0"
+black = "21.9b0"
 certifi = "2021.5.30"
 chardet = "4.0.0"
 click = "8.0.1"
@@ -25,7 +25,7 @@ typed-ast = "1.4.3"
 urllib3 = "1.26.6"
 
 [tool.poetry.dev-dependencies]
-black = {version = "^21.8b0", allow-prereleases = true}
+black = {version = "^21.9b0", allow-prereleases = true}
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]