fixed import on manual test file

Author: HugoMario

samples/client/petstore/python/test/test_model_200_response.py

@@ -16,7 +16,7 @@
 import unittest
 
 import petstore_api
-from petstore_api.models.model_200_response import Model200Response  # noqa: E501
+from petstore_api.models.model200_response import Model200Response  # noqa: E501
 from petstore_api.rest import ApiException