[FIX] purchase: reset reminder status on cancel

Steps to reproduce:

* Create PO
* Confirm Receipt Date
* Cancel PO
* Draft and Confirm again

Current behavior:

* Button for Confirm Receipt Date is not visible

Expected behavior:

* Button for Confirm Receipt Date should be visible

This is happening as we are not resetting the value of `mail_reminder_confirmed` on cancelling PO.

With this commit, we reset value of `mail_reminder_confirmed` so use can Confirm Receipt Date again.

closes odoo/odoo#79122

X-original-commit: 9e48afe5bf4f52b7cc2705fe434b4647df752a59
Signed-off-by: Arnold Moyaux <arm@odoo.com>

addons/purchase/models/purchase.py

@@ -431,7 +431,7 @@ class PurchaseOrder(models.Model):
                 if inv and inv.state not in ('cancel', 'draft'):
                     raise UserError(_("Unable to cancel this purchase order. You must first cancel the related vendor bills."))
 
-        self.write({'state': 'cancel'})
+        self.write({'state': 'cancel', 'mail_reminder_confirmed': False})
 
     def button_unlock(self):
         self.write({'state': 'purchase'})