[FIX] payment: use commercial partner for payments made from payment acquirers

Payments made on eCommerce via a payment acquirer (i.e. Stripe) generate an
"account.payment" record where connected user's "child" partner is used for
partner_id of the payment, instead of commercial partner, as it is done for
payments registered on invoices.

For consistency, commercial partner should also be used for these payments.

opw-2457390

closes odoo/odoo#68003

Signed-off-by: Laurent Smet <smetl@users.noreply.github.com>