Remove build-qa-image step?

Over the past week, the build-qa-image step has failed repeatedly due to Rubygems timeouts (e.g. https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/207284618). I've reported the issue there, but it seems to me this step really shouldn't fail and block the whole test pipeline from running.

@rymai @godfat Can we somehow get rid of this or move this into another stage?

Edit by @rymai: Root Rubygems problem was reported here: https://help.rubygems.org/discussions/problems/36288-frequent-gemremotefetcherunknownhosterror-timed-out-over-the-last-week