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: I900f5702bfa434a53ea0f906ba4d7195249de8b9

zuul.d/project.yaml

@@ -3,7 +3,7 @@
       - publish-openstack-docs-pti
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-xena-jobs
       - check-requirements
       - release-notes-jobs-python3
     check: