Use simpler base image on rubocop job
Summary
While !1734 (merged) introduced rubocop job into our pipeline, the base image on that job is larger than required. The base image should be simpler.
as is
- Total duration: 01:57
- Duration for loading the base image: 01:07
https://gitlab.com/gitlab-org/charts/gitlab/-/jobs/1119414433
to be
- Total duration: 00:33
- Duration for loading the base image: 00:00
https://gitlab.com/gitlab-org/charts/gitlab/-/jobs/1120206128
Edited by Takuya Noguchi