fix: Add comment on classname overriding

Note: we do need to specify the classname, which should be "builtins.tuple":

The serialize method (in airflow/serialization/serializers/builtin.py) does qualname() on the namedtuple, which returns "airflow.providers.databricks.hooks.Row" (the namedtuple dynamically created in the hook). If this is used as classname, it will fail to deserialize: there won't be any deserializer for it.

If we hardcode it to "builtins.tuple", it gets deserialized correctly.

airflow/serialization/serde.py

@@ -136,7 +136,9 @@ def serialize(o: object, depth: int = 0) -> U | None:
     qn = qualname(o)
     classname = None
 
-    # serialize namedtuple like tuples
+    # Serialize namedtuple like tuples
+    # We also override the classname returned by the builtin.py serializer. The classname
+    # has to be "builtins.tuple", so that the deserializer can deserialize the object into tuple.
     if _is_namedtuple(o):
         qn = "builtins.tuple"
         classname = qn