Fix pytype complaint, details below

File "/home/runner/work/monai-deploy-app-sdk/monai-deploy-app-sdk/monai/deploy/core/app_context.py",
  line 49, in update: Type annotation for models does not match type of assignment [annotation-type-mismatch]
  Annotation: monai.deploy.core.models.model.Model (Did you mean 'typing.Optional[monai.deploy.core.models.model.Model]'?)
  Assignment: None
  In assignment of type: Optional[monai.deploy.core.models.model.Model]

Signed-off-by: M Q <mingmelvinq@nvidia.com>

Author: MMelQin

monai/deploy/core/app_context.py

@@ -12,7 +12,7 @@
 from os.path import abspath
 from typing import Dict, Optional
 
-from .models import Model, ModelFactory
+from .models.model import Model, ModelFactory
 from .runtime_env import RuntimeEnv