[FIX] stock_dropshipping: consolidated lines
[FIX] stock_dropshipping: consolidated lines

- Create a SO with 2 lines of the same product (set route as Drop Ship)
- At validation, both lines are merged into a single line in the PO

As a result, one SO line will be over-delivered, and the other
under-delivered.

Two lines should be kept in the PO.

opw-1928702

closes odoo/odoo#30800
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo