try to fix the issue with julia 1.6

Author: klamike

test/nlp_program.jl

@@ -677,9 +677,8 @@ function test_ObjectiveSensitivity_model1()
     MOI.set(model, DiffOpt.ReverseObjectiveSensitivity(), Δf)
     MOI.set(model, DiffOpt.ReverseVariablePrimal(), x, Δp)
 
-    @test_warn "Computing reverse differentiation with both" DiffOpt.reverse_differentiate!(
-        model,
-    )
+    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)
     MOI.set(model, DiffOpt.AllowObjectiveAndSolutionInput(), true)
     @test_nowarn DiffOpt.reverse_differentiate!(model)