Use named argument for ref when calling ReleaseTools::Commits
The constructor for ReleaseTools::Commits requires a named argument for ref
https://gitlab.com/gitlab-org/release-tools/blob/eebcd9824334bc875ef4fa23e2ab48f5aa01a55b/lib/release_tools/commits.rb#L9
Fixes a bug that was introduced with !672 (merged) that was sitting dormant for some time because we didn't up until now trigger the omnibus change logic.
Edited by John Jarvis