Bump Ruby version in Dockerfile for GDK test image
Needed after https://gitlab.com/gitlab-org/gitlab-development-kit/merge_requests/217, because Ruby version in GitLab changed recently.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Needed after https://gitlab.com/gitlab-org/gitlab-development-kit/merge_requests/217, because Ruby version in GitLab changed recently.