[FIX] point_of_sale: set the payment date based on TZ

If a user is in an early timezone (e.g. UTC-5), an order made on the
...-01 19:15:00 or, converted to UTC, as ...-02 00:15:00
fields.Date.today() returns the days ...-02 instead of ...-01
Use context_today to convert in the right timezone.

This slightly change the return format of _payment_fields to return a date
instead of a datetime.

Followup of 7272abe0e3 that was adding the timezone in the context

Closes #22651

addons/point_of_sale/models/pos_order.py

@@ -46,9 +46,11 @@ class PosOrder(models.Model):
         }
 
     def _payment_fields(self, ui_paymentline):
+        payment_date = ui_paymentline['name']
+        payment_date = fields.Date.context_today(self, fields.Datetime.from_string(payment_date))
         return {
             'amount':       ui_paymentline['amount'] or 0.0,
-            'payment_date': ui_paymentline['name'],
+            'payment_date': payment_date,
             'statement_id': ui_paymentline['statement_id'],
             'payment_name': ui_paymentline.get('note', False),
             'journal':      ui_paymentline['journal_id'],
@@ -811,7 +813,7 @@ class PosOrder(models.Model):
         """Create a new payment for the order"""
         args = {
             'amount': data['amount'],
-            'date': data.get('payment_date', fields.Date.today()),
+            'date': data.get('payment_date', fields.Date.context_today(self)),
             'name': self.name + ': ' + (data.get('payment_name', '') or ''),
             'partner_id': self.env["res.partner"]._find_accounting_partner(self.partner_id).id or False,
         }