[FIX] mrp: update quantity after post inventory

Usecase to reproduce:
- Create a BoM with 2 components for a final product
- Create a MO for 100 final products
- Produce 50
- Post Inventory
- Update the MO quantity to 200
- Produce 50 more

The total quantity for components consumed is 175 (instead of 200)

It happens because the update quantity do not take care of existing
produced unit when it updates the raw material moves and their unit
factor. (FYI unit factor is used later in order to know the quantity
to consume depending the produced quantity)

Fix #39866

closes odoo/odoo#39963

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>