Move some CHANGELOG entries to the 8.13.0 part
Spotted while reviewing https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/789/diffs#diff-1
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Spotted while reviewing https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/789/diffs#diff-1