Use LbEnv for style checks and fix formatting
Since we started using python-3-only features, the formatting check fails to format some files: https://gitlab.cern.ch/lhcb/Moore/-/jobs/16671997 . Here the job is migrated to use the python 3 install in LbEnv. The job is even faster now (18 s vs ~25 s before).
Edited by Rosen Matev