Install gm from apt in CI
Despite being a pretty universal solution, compiling Graphicsmagick from the source (!546 (diffs)) is extremely slow and increases the CI test job from ~4 minutes to almost 20 minutes, which may not be acceptable for Workhorse development.
I suggest we installing GM from apt, even if use a newer version than used in Omnibus (1.3.35 vs 1.3.34).
Edited by Aleksei Lipniagov