[DPMSolverSinglestepScheduler] correct `get_order_list` for...

[DPMSolverSinglestepScheduler] correct `get_order_list` for `solver_order=2`and `lower_order_final=True`  (#6953)

* add

* change default

---------
Co-authored-by: yiyixuxu <yixu310@gmail,com>

src/diffusers/schedulers/scheduling_dpmsolver_singlestep.py

@@ -151,7 +151,7 @@ class DPMSolverSinglestepScheduler(SchedulerMixin, ConfigMixin):
         sample_max_value: float = 1.0,
         algorithm_type: str = "dpmsolver++",
         solver_type: str = "midpoint",
-        lower_order_final: bool = True,
+        lower_order_final: bool = False,
         use_karras_sigmas: Optional[bool] = False,
         final_sigmas_type: Optional[str] = "zero",  # "zero", "sigma_min"
         lambda_min_clipped: float = -float("inf"),
@@ -233,7 +233,7 @@ class DPMSolverSinglestepScheduler(SchedulerMixin, ConfigMixin):
                     orders = [1, 2, 3] * (steps // 3) + [1, 2]
             elif order == 2:
                 if steps % 2 == 0:
-                    orders = [1, 2] * (steps // 2)
+                    orders = [1, 2] * (steps // 2 - 1) + [1, 1]
                 else:
                     orders = [1, 2] * (steps // 2) + [1]
             elif order == 1:
@@ -320,7 +320,7 @@ class DPMSolverSinglestepScheduler(SchedulerMixin, ConfigMixin):
 
         if not self.config.lower_order_final and num_inference_steps % self.config.solver_order != 0:
             logger.warn(
-                "Changing scheduler {self.config} to have `lower_order_final` set to True to handle uneven amount of inference steps. Please make sure to always use an even number of `num_inference steps when using `lower_order_final=True`."
+                "Changing scheduler {self.config} to have `lower_order_final` set to True to handle uneven amount of inference steps. Please make sure to always use an even number of `num_inference steps when using `lower_order_final=False`."
             )
             self.register_to_config(lower_order_final=True)