Bump black from 21.8b0 to 21.9b0 (#3123)

* 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>

* Update .pre-commit-config.yaml

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Pascal Vizeli <pvizeli@syshack.ch>

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: 21.8b0
+    rev: 21.9b0
     hooks:
       - id: black
         args:

requirements_tests.txt

@@ -1,4 +1,4 @@
-black==21.8b0
+black==21.9b0
 codecov==2.1.12
 coverage==5.5
 flake8-docstrings==1.6.0