[FIX] models.py: onchange in python2 with 2054b59

Without the call to `super`, with at least two level off expected
onchange return data (eg. `invoice_lines.name`) we have an error in
python2, python3 python implementation of OrderedDict and possibly other
python implementation.

So this worked most often (with python3 CPython C implementation of
OrderedDict) by chance.

closes #25960

odoo/models.py

@@ -5058,6 +5058,7 @@ class BaseModel(MetaModel('DummyModel', (object,), {'_register': False})):
                     }
             """
             def __init__(self, model, dotnames):
+                super(PrefixTree, self).__init__()
                 if not dotnames:
                     return
                 # group dotnames by prefix