Merge branch 'fix-member-role-migration' into 'master'

Remove not null constraint from the namespace

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/137376



Merged-by: Michał Zając <mzajac@gitlab.com>
Approved-by: Max Orefice <morefice@gitlab.com>
Approved-by: Michał Zając <mzajac@gitlab.com>
Reviewed-by: Max Orefice <morefice@gitlab.com>
Co-authored-by: Jarka Košanová <jarka@gitlab.com>