Bump black from 21.11b1 to 21.12b0

Bumps [black](https://github.com/psf/black) from 21.11b1 to 21.12b0.
- [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]

requirements.txt

@@ -1,7 +1,7 @@
 Django>=2.2
 Wagtail>=2.8
 bandit==1.7.1
-black==21.11b1
+black==21.12b0
 flake8==4.0.1
 isort==5.10.1
 msgcheck==3.1