[FIX] stock: select seller date

When the function '_select_seller' in stock warehouse is called, a
datetime is passed to it. But the method needs a date, so we modify it.

OPW-1930264

closes odoo/odoo#30563

addons/stock/models/stock_warehouse.py

@@ -929,7 +929,7 @@ class Orderpoint(models.Model):
             # These days will be substracted when creating the PO
             days += self.product_id._select_seller(
                 quantity=product_qty,
-                date=start_date,
+                date=fields.Date.context_today(self,start_date),
                 uom_id=self.product_uom).delay or 0.0
         date_planned = start_date + relativedelta.relativedelta(days=days)
         return date_planned.strftime(DEFAULT_SERVER_DATETIME_FORMAT)