Bump black from 21.5b2 to 21.6b0 (#1374)

Bumps [black](https://github.com/psf/black) from 21.5b2 to 21.6b0.
- [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
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[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==21.5b2",
+            "black==21.6b0",
             "pytest-timeout>=1.4.2,<1.5",
             "trustme>=0.7,<0.8",
         ],