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: I3a715d59a40eb965b870252335ee73c0da781919

.zuul.yaml

@@ -1,6 +1,6 @@
 - project:
     templates:
       - openstack-cover-jobs
-      - openstack-python3-xena-jobs
+      - openstack-python3-yoga-jobs
       - release-notes-jobs-python3
       - publish-openstack-docs-pti