Require Source in Members::UpdateService Again

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168097



Merged-by: Pedro Pombeiro <noreply@pedro.pombei.ro>
Approved-by: Pedro Pombeiro <noreply@pedro.pombei.ro>
Reviewed-by: Pedro Pombeiro <noreply@pedro.pombei.ro>
Co-authored-by: Jason Goodman <jgoodman@gitlab.com>