Switch to py38 for horizon-non-primary-django-jobs
Switch to py38 for horizon-non-primary-django-jobs

The template for victoria does not include py37, so switch
horizon-non-primary-django-jobs to use py38 as newest version to avoid
an extra job to run.

Change-Id: I32b10cc726254dde3c10f2df2e392d29c4108d2f

ChameleonCloud/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon,openstack/horizon,ChameleonCloud/horizon,openstack/horizon,openstack/horizon,openstack/horizon