Add Python3 yoga unit tests

This patch updates the project template to use the Yoga project template
to ensure unit testing is in place for all of the tested runtimes
for yoga. For more please refer to [1].

[1]: https://governance.openstack.org/tc/reference/project-testing-interface.html

Change-Id: I47f85706b2b5ad8ac12ac67e97b5bb7179572615

.zuul.yaml

@@ -3,7 +3,7 @@
       - check-requirements
       - lib-forward-testing-python3
       - openstack-cover-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-yoga-jobs
       - periodic-stable-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3