Switch testing to Yoga testing runtime

Upating the tetsing template to Yoga testing runtime:
https://governance.openstack.org/tc/reference/runtimes/yoga.html

Change-Id: Ibe5599895d6e41a4c3efda1ba8d47369b4f8e6b6

.zuul.d/jobs.yaml

@@ -1,7 +1,7 @@
 - project:
     templates:
       - openstack-python35-jobs
-      - openstack-python3-xena-jobs
+      - openstack-python3-yoga-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check: