Stop Barbarian Leaders from defending each other
Split from #41938
Units for which ransom would be paid should not defend each other. #41938 has a proposed patch.
One issue I see with that patch is that it treats "leader + nuke" different from "nuke + leader". If leader gets selected as the defender, ransom is paid for both units. If the nuke gets selected as the defender, no ransom is paid.
Rule change, so targeting to S3_0 at the earliest.