Test fails for python version 3.5.* < 3.5.2
The test (on current drone) is affected by https://bugs.python.org/#25195, see https://drone.tryton.org/trypod.tryton.org/tryton/modules.notification_email/default/82473800eabdc303b69dfca55e54549e623371e8
I propose the simple solution to skip the test on affected versions.