[tests] use parent class for monkey patching to not break other tests (#4088)

* [tests] use parent class for monkey patching to not break other tests

* fix

tests/pipelines/stable_diffusion_xl/test_stable_diffusion_xl.py

@@ -230,10 +230,13 @@ class StableDiffusionXLPipelineFastTests(PipelineLatentTesterMixin, PipelineTest
         pipe_2 = StableDiffusionXLImg2ImgPipeline(**components).to(torch_device)
         pipe_2.unet.set_default_attn_processor()
 
-        def assert_run_mixture(num_steps, split, scheduler_cls):
+        def assert_run_mixture(num_steps, split, scheduler_cls_orig):
             inputs = self.get_dummy_inputs(torch_device)
             inputs["num_inference_steps"] = num_steps
 
+            class scheduler_cls(scheduler_cls_orig):
+                pass
+
             pipe_1.scheduler = scheduler_cls.from_config(pipe_1.scheduler.config)
             pipe_2.scheduler = scheduler_cls.from_config(pipe_2.scheduler.config)
 
@@ -287,10 +290,13 @@ class StableDiffusionXLPipelineFastTests(PipelineLatentTesterMixin, PipelineTest
         pipe_3 = StableDiffusionXLImg2ImgPipeline(**components).to(torch_device)
         pipe_3.unet.set_default_attn_processor()
 
-        def assert_run_mixture(num_steps, split_1, split_2, scheduler_cls):
+        def assert_run_mixture(num_steps, split_1, split_2, scheduler_cls_orig):
             inputs = self.get_dummy_inputs(torch_device)
             inputs["num_inference_steps"] = num_steps
 
+            class scheduler_cls(scheduler_cls_orig):
+                pass
+
             pipe_1.scheduler = scheduler_cls.from_config(pipe_1.scheduler.config)
             pipe_2.scheduler = scheduler_cls.from_config(pipe_2.scheduler.config)
             pipe_3.scheduler = scheduler_cls.from_config(pipe_3.scheduler.config)