"Widen" `T>:Any` to `Any` in `simple_join`.
I gave up fixing the deep stack overflow.
Making the `env` soundness seems much easier.
close #47874.
At present, we only catch cases with pattern like
A1 = Union{T,Int} where {T}
A2 = Union{T2,Int} where {T,T2<:Union{T,Int}}
A3 = Union{Int,A2}
