can_setindex for <:MArray evaluates to false

[jecs]

As the title suggests, can_setindex(::Type{<:StaticArrays.MArray}) evaluates to false, even though setindex! is defined for MArray.

Suggested fix:

ArrayInterface.can_setindex(::Type{<:StaticArrays.MArray}) = true

[ChrisRackauckas]

Yes that should be changed./

[Tokazama]

@jecs , this should be a pretty straightforward PR. If you make one I'd be happy to review it (make sure to tag me to get my attention though).