Prevent repeat rerunning of RAVEN sky map comparsion

Currently we rerun skymap comparison/RAVEN pipeline whenever a new sky map is uploaded to the superevent or external event. However, this will often occur twice in the superevent since the multiordered and flattened equivalent will be uploaded around the same time, and both use the multiordered sky map in the calculation: https://git.ligo.org/emfollow/gwcelery/-/blob/b8322e10d5023f217b71a3ccaf90dd92efe23210/gwcelery/tasks/external_triggers.py#L357

We should fix this by only re-triggering of multiorder sky maps in the superevent, but allow flattened for external trigger. There may also be a better fix than this as well.