Running Ruby linter for GettingStarted

GettingStarted has browser tests since
https://gerrit.wikimedia.org/r/#/c/123873

Job added in jenkins-job-builder-config by:
    https://gerrit.wikimedia.org/r/156510

Bug: 52246
Change-Id: I94bc8dd6b569a6f6353b66429e2aa1118db3b995