Fix innocent non-transitivity of chain order related to issue numbers

As explained in the document in https://github.com/IntersectMBO/ouroboros-consensus/pull/891 (sections "Current chain order is non-transitive" and "Regarding opcert numbers"), the current chain order is not transitive in a particular edge case related to issue numbers, but this is relatively simple (though non-obvious) to fix this as also explained there.

Also see https://github.com/IntersectMBO/ouroboros-consensus/pull/1063#discussion_r1576764055