Some payment tests were unexpectedly relying on the 'transfer' payment acquirer
to work because of a multi-company issue in the core payment tests setup.
This commit fixes the problem and adds an additional check in the tests to
make sure they rely correctly on the 'dummy' acquirer created in the payment
tests common.
closesodoo/odoo#94972
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>