Subtyping bug for complicated type alias

[andreasnoack]

We use a slightly complicated type alias in the linear algebra code and it appears the <: is getting the ralation wrong for complex matrices.

julia> LinAlg.RealHermSymComplexHerm
Union{Hermitian{Complex{T<:Real},S},Hermitian{T<:Real,S},Symmetric{T<:Real,S}}

julia> Symmetric{Float64,Matrix{Float64}} <: LinAlg.RealHermSymComplexHerm
true

julia> Hermitian{Float64,Matrix{Float64}} <: LinAlg.RealHermSymComplexHerm
true

julia> Hermitian{Complex{Float64},Matrix{Complex{Float64}}} <: LinAlg.RealHermSymComplexHerm
false

[JeffBezanson]

closed by #18457