Bump black from 21.7b0 to 21.8b0 in /python/requirements/CI-complete

Bumps [black](https://github.com/psf/black) from 21.7b0 to 21.8b0.
- [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]

python/requirements/CI-complete/requirements.txt

@@ -1,5 +1,5 @@
 biopython==1.79
-black==21.7b0
+black==21.8b0
 coverage==5.5
 flake8==3.9.2
 h5py==3.4.0