[FIX] sale_coupon: batch confirmation of sales orders

`_send_reward_coupon_mail` is defined as `ensure_one` but is called on
`self` in `action_confirm` which supports multiple records in self, thus
raising a ValueError when confirming multiple sales orders together.

This commit adapts the method to handle multiple records.

FW-Port of odoo/enterprise#12161

closes odoo/odoo#56861

X-original-commit: 99c230c1c167d7369f8003c0219386799f92097d
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>
Co-authored-by: Alex Comba <alex.comba@agilebg.com>

addons/sale_coupon/models/sale_order.py

@@ -240,12 +240,13 @@ class SaleOrder(models.Model):
     def _send_reward_coupon_mail(self):
         template = self.env.ref('coupon.mail_template_sale_coupon', raise_if_not_found=False)
         if template:
-            for coupon in self.generated_coupon_ids:
-                self.message_post_with_template(
-                    template.id, composition_mode='comment',
-                    model='coupon.coupon', res_id=coupon.id,
-                    email_layout_xmlid='mail.mail_notification_light',
-                )
+            for order in self:
+                for coupon in order.generated_coupon_ids:
+                    order.message_post_with_template(
+                        template.id, composition_mode='comment',
+                        model='coupon.coupon', res_id=coupon.id,
+                        email_layout_xmlid='mail.mail_notification_light',
+                    )
 
     def _get_applicable_programs(self):
         """