Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23079 and https://gitlab.com/gitlab-org/gitlab-ce/issues/34412
Replaces https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8662
/cc @stanhu @yorickpeterse @to1ne @zj