support 1.6

https://docs.julialang.org/en/v1.6/stdlib/Test/#:~:text=Use%20%40test%5Flogs%20instead

Author: klamike

test/nlp_program.jl

@@ -677,8 +677,8 @@ function test_ObjectiveSensitivity_model1()
     MOI.set(model, DiffOpt.ReverseObjectiveSensitivity(), Δf)
     MOI.set(model, DiffOpt.ReverseVariablePrimal(), x, Δp)
 
-    warning = "Computing reverse differentiation with both solution sensitivities and objective sensitivities. Set `DiffOpt.AllowObjectiveAndSolutionInput()` to `true` to silence this warning."
-    @test_warn warning DiffOpt.reverse_differentiate!(model)
+    msg = "Computing reverse differentiation with both solution sensitivities and objective sensitivities. Set `DiffOpt.AllowObjectiveAndSolutionInput()` to `true` to silence this warning."
+    @test_logs (:warn, msg) DiffOpt.reverse_differentiate!(model)
     MOI.set(model, DiffOpt.AllowObjectiveAndSolutionInput(), true)
     @test_nowarn DiffOpt.reverse_differentiate!(model)