[FIX] coupon: allow overridden method to be called

Due to some changes in the ORM, the previous implementation doesn't allow the override of a method to be called.

closes odoo/odoo#83595

X-original-commit: b1af44bad3a87a92f8726ed69eadffdbe4ac7c0b
Signed-off-by: Masereel Pierre <pim@odoo.com>
Signed-off-by: Trinh Jacky (trj) <trj@odoo.com>

addons/coupon/models/coupon.py

@@ -24,7 +24,7 @@ class Coupon(models.Model):
          """
         return str(random.getrandbits(64))
 
-    code = fields.Char(default=_generate_code, required=True, readonly=True)
+    code = fields.Char(default=lambda self: self._generate_code(), required=True, readonly=True)
     expiration_date = fields.Date('Expiration Date', compute='_compute_expiration_date')
     state = fields.Selection([
         ('reserved', 'Pending'),