Improvements to admin/users feature specs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/140218



Merged-by: Drew Blessing <drew@gitlab.com>
Approved-by: Smriti Garg <sgarg@gitlab.com>
Approved-by: Drew Blessing <drew@gitlab.com>
Co-authored-by: Imre Farkas <ifarkas@gitlab.com>