Runner ability to fetch refs for merge request pipelines
gitlab-org/gitlab-ee#7380 will introduce building combined refs for merge request pipelines.
GitLab will need to schedule jobs for
refs/merge-requests/:iid:/merge ref that is outside of the default cloning ref-spec.
Today users can control how they retrieve source code (
none). Given there's no way to clone outside of the default ref-spec, we will force a
fetch mode in case of merge request pipeline.
- PoC: !1092 (closed)