[FIX] stock: relax SN quant restriction

Backport of
https://github.com/odoo/odoo/commit/274dd3bf503e1b612179db92e410b336bfaecfb4


(v15)

Steps to reproduce:
- create a product with tracking = 'lot'
- create a receipt for the product with a done qty > 1 for 1 lot
- change tracking of product to 'serial'
- go to "Update Quantity" and try to update the existing quant
  inventory_quantity to 0

Expected Result:
It's possible to make the quant 0

Actual Result:
Confusing Validationerror occurs:
"A serial number should only be linked to a single product."

Error occurs because the corresponding Inventory adjustment location is
not allowed to have more than quant.quantity > 1 so the user is never
able to remove more than 1 of the quantity from their stock.

opw-3062017

closes odoo/odoo#106996

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