[FIX] website_sale_coupon: correctly update free shipping on cart
[FIX] website_sale_coupon: correctly update free shipping on cart

Promotion programs can be added in 3 ways, no_code_promo_program_ids,
code_promo_program_id, and through applied_coupon_ids.
So free delivery obtained by the two latter would not correctly update
the cart page, because the result of _get_free_shipping_lines would be
empty.

closes odoo/odoo#40317

Forward-port-of: https://github.com/odoo/enterprise/pull/6663
X-original-commit: bfde75dd72d1e529bfb93d2b83b22b8c2f0fcea1
Signed-off-by: Nans Lefebvre (len) <a573b540d2dde90ba6da3b9d6286c8ec60c10044@odoo.com>

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