Bump black from 21.6b0 to 21.7b0

Bumps [black](https://github.com/psf/black) from 21.6b0 to 21.7b0.
- [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] <[email protected]>

Author: dependabot[bot]

poetry.lock

@@ -11,7 +11,7 @@ python = "^3.9"
 invoke = "1.6.0"
 pytest = "6.2.4"
 
-black = { version = "^21.6b0", allow-prereleases = true }
+black = { version = "^21.7b0", allow-prereleases = true }
 codespell = ">=2.0.0"
 flake8 = "^3.9.2"
 pep8-naming = "^0.12.0"