Following the steps that changed every quantity in a matrix, the next
step was triggered after at least one sale order line's quantity was
changed. Due to the number of lines created, one of the so lines was
sometimes not updated before the next step, which produces an error in
the final sale_count.

In order to check the total and ensure every line was updated, we set
the partner sooner in the tour, which in turn sets the pricelist used to
get the price of each line. Thus allowing a check on the subtotal.

Backport of commit-af1e67aa2c6c676479ee4ea73106bcabd20c621e

closes odoo/odoo#100273

Signed-off-by: Morgane Demesmaeker <edm@odoo.com>