implemented changes from PR review

Author: michaelraczycki

tests/sampling/test_mcmc.py

@@ -827,11 +827,12 @@ def test_step_vars_in_model(self):
             with pytensor.config.change_flags(mode=fast_unstable_sampling_mode):
                 step1 = NUTS([c1])
                 step2 = NUTS([c2])
-                step2.vars = [
-                    at.dscalar("x"),
-                ]
+                step2.vars = [c2]
                 step = CompoundStep([step1, step2])
-                with pytest.raises(ValueError):
+                with pytest.raises(
+                    ValueError,
+                    match=r".* assigned to .* sampler is not a value variable in the model. You can use `util.get_value_vars_from_user_vars` to parse user provided variables.",
+                ):
                     assign_step_methods(model, step)