[FIX] stock: traceback during PO import

Following #127245

It happens because `_should_bypass_reservation` has been removed in 15.0
and only exist on the `stock.move` object and not the `stock.move.line`
anymore

opw-3336131

closes odoo/odoo#129054

X-original-commit: 7e917e8713e246811531f9d7c90395242e544057
Signed-off-by: William Henrotin (whe) <whe@odoo.com>