Add a test to avoid #53054 regressions

stdlib/LinearAlgebra/test/blas.jl

@@ -135,6 +135,19 @@ Random.seed!(100)
             a[begin] = elty(NaN)
             @test BLAS.nrm2(a) === abs2(elty(NaN))
         end
+        @testset "deterministic mul!" begin
+            # mul! should be deterministic, see #53054
+            function tester_53054()
+                C = ComplexF32
+                mat = zeros(C, 1, 1)
+                for _ in 1:100
+                    v = [C(1-0.2im) C(2+0.3im)]
+                    mul!(mat, v, v', C(1+im), 1)
+                end
+                return mat
+            end
+            @test allequal(tester_53054() for _ in 1:10000)
+        end
         @testset "scal" begin
             α = rand(elty)
             a = rand(elty,n)