restrict vec(::Transpose) shortcut to numbers (#40502)

Author: mcabbott

stdlib/LinearAlgebra/src/adjtrans.jl

@@ -238,7 +238,7 @@ similar(A::AdjOrTrans, ::Type{T}, dims::Dims{N}) where {T,N} = similar(A.parent,
 
 # sundry basic definitions
 parent(A::AdjOrTrans) = A.parent
-vec(v::TransposeAbsVec) = parent(v)
+vec(v::TransposeAbsVec{<:Number}) = parent(v)
 vec(v::AdjointAbsVec{<:Real}) = parent(v)
 
 ### concatenation

stdlib/LinearAlgebra/test/adjtrans.jl

@@ -275,6 +275,9 @@ end
     @test vec(Transpose(intvec)) === intvec
     cvec = [1 + 1im]
     @test vec(cvec')[1] == cvec[1]'
+    mvec = [[1 2; 3 4+5im]];
+    @test vec(transpose(mvec))[1] == transpose(mvec[1])
+    @test vec(adjoint(mvec))[1] == adjoint(mvec[1])
 end
 
 @testset "horizontal concatenation of Adjoint/Transpose-wrapped vectors and Numbers" begin