Group Issue Board should retrieve scoped labels

Created by: giuliohome

With an EE license, the group issue boards should allow the import of scoped labels. Currently, the scoped labels are missing at https://github.com/xanzy/go-gitlab/blob/main/group_boards.go#L37. However, the update at https://github.com/xanzy/go-gitlab/blob/main/group_boards.go#L148 includes scoped labels and functions as expected.