Add 'black' to test-requirements.txt
Add 'black' to test-requirements.txt to ensure that it is available
when scripts/check is run during CI. Pin to newest version that works
with Debian Buster.
Bug: T351605
Related MRs:
- !197 (merged)
- !195 (merged) (This MR)
- master
Edited by Ahmon Dancy