Minor improvement to inference of ntuple (JuliaLang#54544)

In the non-`@generated` branch, where `N` may be unknown, assert its
type as `Int` so that the type of the created range can be inferred.

base/ntuple.jl

@@ -72,7 +72,7 @@ julia> ntuple(i -> 2*i, Val(4))
     if @generated
         :(@ntuple $N i -> f(i))
     else
-        Tuple(f(i) for i = 1:N)
+        Tuple(f(i) for i = 1:(N::Int))
     end
 end
 typeof(function ntuple end).name.max_methods = UInt8(5)

test/tuple.jl

@@ -532,6 +532,8 @@ end
     for n = 0:15
         @test ntuple(identity, Val(n)) == ntuple(identity, n)
     end
+
+    @test Core.Compiler.return_type(ntuple, Tuple{typeof(identity), Val}) == Tuple{Vararg{Int}}
 end
 
 struct A_15703{N}