release note for UpperHessenberg (#44326)

add note that UpperHessenberg was introduced in 1.3

Author: lucaferranti

stdlib/LinearAlgebra/src/hessenberg.jl

@@ -9,6 +9,9 @@
 Construct an `UpperHessenberg` view of the matrix `A`.
 Entries of `A` below the first subdiagonal are ignored.
 
+!!! compat "Julia 1.3"
+    This type was added in Julia 1.3.
+
 Efficient algorithms are implemented for `H \\ b`, `det(H)`, and similar.
 
 See also the [`hessenberg`](@ref) function to factor any matrix into a similar