[FIX] pos_sale: Correctly set manually_set_price on settle order

Current behavior:
When settling an order, the manually_set_price field is set to true
when it shoudln't. This cause issues in the french localization, as it
was always showing the current price as the old price.

Steps to reproduce:
- Install the l10n_fr_pos_cert module, and pos_sale
- Create a new order, add a product and confirm the order
- Open the PoS
- Settle the order you created
- The current price is shown as the old price

opw-3440797

closes odoo/odoo#133382

Signed-off-by: Robin Heinz (rhe) <rhe@odoo.com>