[FIX] delivery: shipping carrier is set after delivery generated

Before this commit
==================
when SO is confirmed and Delivery is created then add the shipping method
in SO, in this case, the shipping carrier is not set in the existing undelivered
delivery of that SO.

After this commit
=================
So in this commit, we set the shipping carrier for undelivered delivery.

taskId - 2946360

closes odoo/odoo#121300

X-original-commit: 51523c0dbf6ce9dd1a1ff35e03fa6a51267da14b
Signed-off-by: Tiffany Chang <tic@odoo.com>