Update test/matmul.jl

Co-authored-by: Jishnu Bhattacharya <[email protected]>

Author: araujoms

test/matmul.jl

@@ -550,7 +550,7 @@ end
         D = Matrix(Hermitian(A * A'))
         @test mul!(copy(D), A, A', true, 3) ≈ 4D
         if T <: Complex
-            @test mul!(copy(C), A', A, im, 2) ≈ 2C + im*C
+            @test mul!(2C, A', A, im, 2) ≈ (4 + im) * C
             @test mul!(copy(D), A, A', im, 3) ≈ 3D + im*D
         end
     end