Merge branch 'black-diff' into 'master'

CI: add --diff to black

See merge request !27
2 jobs for master in 3 minutes and 35 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #28743
pyFstat
pytest

00:03:26

 
  Static Analysis
passed #28744
pyFstat
static

00:00:09