[FIX] stock: forecast button color

Steps to reproduce:
- Enable multistep routes (3 steps delivery)
- Create a new storable product (0 on hand quantity)
- Confirm an SO with that product

Bug:
forecast button is correctly red on the SO line but it's green on the
stock pickings

Fix:
button should be green if it's possible to reserve quantity red otherwise

opw-3440627

closes odoo/odoo#134335

Signed-off-by: Quentin Wolfs (quwo) <quwo@odoo.com>