Merge branch '346563_refactor_fork_service_tests' into 'master'

Refactor ForkService tests

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/141003



Merged-by: Patrick Cyiza <jpcyiza@gitlab.com>
Approved-by: Patrick Cyiza <jpcyiza@gitlab.com>
Approved-by: Eduardo Bonet <ebonet@gitlab.com>
Co-authored-by: Vasilii Iakliushin <viakliushin@gitlab.com>