Bump black from 20.8b1 to 21.4b2 (#1313)

Bumps [black](https://github.com/psf/black) from 20.8b1 to 21.4b2.
- [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-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

setup.py

@@ -73,7 +73,7 @@ setup(
             "pytest-xdist>=2.2.1,<2.3",
             "pytest-asyncio>=0.10,<0.16",
             "beautifulsoup4>=4.8.1,<4.10.0",
-            "black==20.8b1",
+            "black==21.4b2",
             "pytest-timeout>=1.4.2,<1.5",
             "trustme>=0.7,<0.8",
         ],