ENHANCE: Special redispatch for Nat.Hom.ByNS if group is found out to…

… be finite

This is needed, as for matrix groups the earlier `NiceMonomorphism` dispatch does not hold.
Test is only done before expesive action search is started, so negligible cost.

Also added redispatches in case the NiceMonomorphism approach is ever removed.

This fixes gap-system#3070

Added testfile