Align text fixture with Pipeline.grouped_nodes_by_namespace behavior

Signed-off-by: Laura Couto <laurarccouto@gmail.com>

Author: lrcouto

kedro-airflow/tests/test_node_grouping.py

@@ -241,10 +241,10 @@ def test_is_memory_dataset(
                 "namespace3": ["namespace3.f5"],
             },
             {
-                "__default__": [],
+                "__default__": ["namespace2", "namespace1"],
                 "namespace1": [],
                 "namespace2": ["namespace1"],
-                "namespace3": ["namespace2"],
+                "namespace3": ["namespace1"],
             },
         ),
     ],