loosen restriction on input array for cache type assertion

[jrevels]

This fixes an accidental regression in our support of non-Array ForwardDiff inputs (thanks for pointing this out, @tkelman).

I'm a tad concerned that this might damage performance for non-AbstractArray inputs, since the fallback here uses the result of ndims in a type parameter.

It would be nice if there were something like similar_type we could call on array-likes, which would allow us to generalize the array types used by the cache types.

[tkelman]

thank pkgeval, and keep an eye on the pulse page the day after you tag