Share project with public groups i'm not member of

Hey there,

why are public groups not listen in the ‘Share with group’ list of the project settings page?
https://gitlab.open-xchange.com///settings/members

In our scenario we have LDAP groups for each department that are synced with corresponding groups on our GitLab instance. What we trying to achieve is that masters/owners of a project can also add groups that they aren’t member of. (think of a ‘qa’ project should be shared with ‘mobile-native’ department).

docs: https://docs.gitlab.com/ee/workflow/share_projects_with_other_groups.html
hint in an issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/33349#note_31600103