[FIX] website_sale_wishlist: fix undeterministic error in tour

This commit attempts to fix an undeterministic error during one of
`website_sale_wishlist` tests.
Due to a race condition it may happen that the button to add to the
wishlist would be re enabled while it should be disabled (if the product
is already in the wishlist) causing the tour to fail.

closes odoo/odoo#98143

Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>