Add Python3 xena unit tests

This is an automatically generated patch to ensure unit testing
is in place for all the of the tested runtimes for xena.

See also the PTI in governance [1].

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

Change-Id: I59a2a1e00b148f20e5a01dced5dc818a56ed5056

zuul.d/project.yaml

@@ -2,7 +2,7 @@
 - project:
     templates:
       - openstack-cover-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-xena-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check: