test: order in first case too

Author: DhairyaLGandhi

test/downstream/observables_autodiff.jl

@@ -34,7 +34,7 @@ sol = solve(prob, Tsit5())
         sum(sol[sys.w])
     end
     du_ = [1.0, 1.0, 1.0, 0.0]
-    du = [du_ for _ in sol.u]
+    du = [du_ for _ in sol[[D(x), x, y, z]]]
     @test du == gs.u
 
     # Observable in a vector