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: I800e6f273412671239eabd7d5e86b5ba7acd3745
diff --git a/.zuul.yaml b/.zuul.yaml
index 5b54009..01f3f60 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -216,7 +216,7 @@
 - project:
     templates:
       - openstack-cover-jobs
-      - openstack-python3-xena-jobs
+      - openstack-python3-yoga-jobs
       - check-requirements
       - publish-openstack-docs-pti
       - release-notes-jobs-python3