[NFC] polish colossalai/engine/schedule/_pipeline_schedule.py code style (#2744)

colossalai/engine/schedule/_pipeline_schedule.py

@@ -4,8 +4,9 @@
 import inspect
 from typing import Callable, List, Tuple, Union
 
-import colossalai.communication as comm
 import torch.cuda
+
+import colossalai.communication as comm
 from colossalai.amp.naive_amp import NaiveAMPModel
 from colossalai.context.parallel_mode import ParallelMode
 from colossalai.core import global_context as gpc
@@ -157,6 +158,7 @@ class PipelineSchedule(BaseSchedule):
 
     def pre_processing(self, engine):
         from colossalai.zero.sharded_model.sharded_model_v2 import ShardedModelV2
+
         # TODO: remove this after testing new zero with pipeline parallelism
         model = engine.model
         if isinstance(model, NaiveAMPModel):