[FIX] pos_restaurant_adyen: fix typo in method name

The function `get_adyen_endpoints` was renamed to `_get_adyen_endpoints`
It was a typo in the method name, so it was not called and a traceback
was raised.

closes odoo/odoo#130396

Signed-off-by: Robin Heinz (rhe) <rhe@odoo.com>