Merge branch 'pl-run-syntax-checks-only-on-backend-changes' into 'master'

CI: Run Ruby syntax checks only on Ruby related changes

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143551



Merged-by: Lin Jen-Shin <jen-shin@gitlab.com>
Approved-by: Lin Jen-Shin <jen-shin@gitlab.com>
Co-authored-by: Peter Leitzen <pleitzen@gitlab.com>