Merge branch 'finalize-group-member-namespace-id-migration' into 'master'

Finalize group member namespace id migration

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/105288



Merged-by: Adam Hegyi <ahegyi@gitlab.com>
Approved-by: Adam Hegyi <ahegyi@gitlab.com>
Co-authored-by: Serena Fang <sfang@gitlab.com>