Add StaticArrays.SOneTo to known_last examples, to give an example of it doing something other than returning nothing.

Author: chriselrod

README.md

@@ -103,7 +103,8 @@ returns `one(Int)`.
 ## known_last(::Type{T})
 
 If `last` of instances of type `T` are known at compile time, return that
-last element. Otherwise, return `nothing`.
+last element. Otherwise, return `nothing`. For example,
+`known_last(StaticArrays.SOneTo{4})` returns 4.
 
 ## known_step(::Type{T})
 

src/ArrayInterface.jl

@@ -509,6 +509,8 @@ If `last` of an instance of type `T` is known at compile time, return it.
 Otherwise, return `nothing`.
 
 @test isnothing(known_last(typeof(1:4)))
+using StaticArrays
+@test known_last(typeof(SOneTo(4))) == 4
 """
 known_last(::Any) = nothing
 """