Skip to install rubocop in non-rubocop jobs
What
This MR enables us to skip to install rubocop in non-rubocop jobs.
Bundler :rubocop
group was already prepared in !2358 (merged).
Why
To speed up omnibus-gitlab CI pipelines.
Closes #3270 (closed)
Part of #3269 (closed)
Edited by GitLab Release Tools Bot