There are various shows where the only (guest) cast will be voice actors, predominantly animation/cartoons & anime.
I don't see much point in giving a choice as to whether it's a voice role or not for these types of shows which is why I propose that a checkbox be added on shows - it would be up to TVMaze to decide who can change it.
If set, The credit is for a voice only should be either locked (or alternatively enabled by default).
