[FIX] stock: expected singleton issue in quants when lot/sn number

If applied, this commit will solve the issue of the singleton when there are 2
quants with the same location and same products but one quant with a lot and
another quant without a lot number.

Steps to produce:
- Create one quant with location-1 and without lot number.
- Create another quant with location-1 but with the lot number.
- Create 3rd quant with location-1 with same lot number as step2.
The error will raise in 3rd step as it is not accepting the 2 quants where one
is with lot number and another is without lot number.

see - https://tinyurl.com/2hqrgmwm

sentry - 4024572562

closes odoo/odoo#119152

X-original-commit: 05a7f5c04804423cfc3a833a1b3f0b5eec3fc147
Signed-off-by: Tiffany Chang <tic@odoo.com>

addons/stock/models/stock_quant.py

@@ -803,7 +803,7 @@ class StockQuant(models.Model):
                 self.product_id, self.location_id, lot_id=self.lot_id,
                 package_id=self.package_id, owner_id=self.owner_id, strict=True)
             if quant:
-                self.quantity = quant.quantity
+                self.quantity = quant.filtered(lambda q: q.lot_id == self.lot_id).quantity
 
             # Special case: directly set the quantity to one for serial numbers,
             # it'll trigger `inventory_quantity` compute.