fix: set sagemaker_config=None on mock session in test_from_jumpstart_config_applies_volume_size (#5882)

fix unit test sm-serve

Author: lucasjia-aws

sagemaker-serve/tests/unit/test_model_builder_coverage_boost.py

@@ -424,6 +424,7 @@ def test_from_jumpstart_config_applies_volume_size(self, mock_deploy_kwargs):
 
         mock_session = Mock()
         mock_session.boto_region_name = "us-west-2"
+        mock_session.sagemaker_config = None
 
         mb = ModelBuilder.from_jumpstart_config(
             jumpstart_config=js_config,