[FIX] purchase_requisition: fix singleton error

Activate Product variants and create a new products with attributes Legs, Size and color.

Now enable Variant Grid Entry and Purchase Agreements from purchase settings and now create a Blanket Order from Purchase -> Orders -> Blanket Orders with any products from above created variants.

Confirm the created blanked order and click on New Quotation, now a new RFQ will be created, and click on add an item button and select the product we have created before, now Choose Product Variants matrix will be opened. Enter some random quantities in multiple lines and click on confirm button.

Exception will be raised

closes odoo/odoo#106507

Signed-off-by: Tiffany Chang <tic@odoo.com>

addons/purchase_requisition/models/purchase.py

@@ -259,7 +259,7 @@ class PurchaseOrderLine(models.Model):
                     params = {'order_id': pol.order_id}
                     seller = pol.product_id._select_seller(
                         partner_id=partner,
-                        quantity=self.product_qty,
+                        quantity=pol.product_qty,
                         date=pol.order_id.date_order and pol.order_id.date_order.date(),
                         uom_id=line.product_uom_id,
                         params=params)