[FIX] fields: conversion of Many2oneReference value

The value of that field can be given as a dict containing the fields of
the corresponding record.

Co-authored with Michael Mattiello <mcm@odoo.com>

closes odoo/odoo#36779

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

odoo/fields.py

@@ -2470,8 +2470,7 @@ class Many2oneReference(Integer):
         # cache format: id or None
         if isinstance(value, BaseModel):
             value = value._ids[0] if value._ids else None
-
-        return value
+        return super().convert_to_cache(value, record, validate)
 
     def _remove_inverses(self, records, value):
         # TODO: unused