Optimise `rspec:coverage`
What does this MR do?
This optimizes the rspec:coverage
job by not using the Rails cache, and only install the gems needed.
This saves about 3 minutes compared to https://app.periscopedata.com/app/gitlab/652085/Engineering-Productivity---Pipeline-Build-Durations?widget=7248745&udv=1005715.
Example: https://gitlab.com/gitlab-org/gitlab/-/jobs/739119555
Closes #247457 (closed).
Edited by Rémy Coutable