Missed leaf type canonicalization

[TotalVerb]

The leaf types Tuple{Int} and Tuple{T} where T <: Int aren't canonicalized to the same thing.

julia> Tuple{Int} == (Tuple{T} where T <: Int)
true

julia> Tuple{Int} === (Tuple{T} where T <: Int)
false

julia> Tuple{Int} isa Type{Tuple{T} where T <: Int}
false

[JeffBezanson]

This was noted in #19998. Also, isleaftype(Tuple{T} where T <: Int) is false, so this has not been a major issue in practice so far.

[TotalVerb]

OK, no point duplicating this issue then.