Add roles omit-when-absent assertions to round-trip tests

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: ethinallen

tests/test_models_round_trip.py

@@ -16857,6 +16857,7 @@ def test_user_organization_membership_base_list_data_omits_absent_optional_non_n
         }
         instance = UserOrganizationMembershipBaseListData.from_dict(data)
         serialized = instance.to_dict()
+        assert "roles" not in serialized
         assert "organization_name" not in serialized
         assert "custom_attributes" not in serialized
 
@@ -17542,6 +17543,7 @@ def test_organization_membership_omits_absent_optional_non_nullable_fields(self)
         }
         instance = OrganizationMembership.from_dict(data)
         serialized = instance.to_dict()
+        assert "roles" not in serialized
         assert "organization_name" not in serialized
         assert "custom_attributes" not in serialized