[FIX] sale_coupon: fix concurrent update on cart
[FIX] sale_coupon: fix concurrent update on cart

Shop page link and popover use the same route which make a write on db
to recompute coupon lines. Can lead to concurent updates if unlucky on
timing.

closes odoo/odoo#39356

X-original-commit: 14253c412be8078290e808fe255c746afa79cc9c
Signed-off-by: Quentin Smetz (qsm) <75b324bb495ac8d4f83496f7c52eda774af7ed7a@odoo.com>

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