Add non-voting Python 3.10 jobs for Zed cycle

The template which is used to test runtime for the Zed cycle added
python 3.10 as a non-voting job [1]. So this patch follows the same
thing here.

[1] https://review.opendev.org/c/openstack/openstack-zuul-jobs/+/831633

Change-Id: Ibbd3fa8804f70a5644af10c105f764fd65b44086

.zuul.yaml

@@ -49,6 +49,8 @@
       - openstack-tox-py37
       - openstack-tox-py38
       - openstack-tox-py39
+      - openstack-tox-py310:
+          voting: false
       - stackviz-nodejs10-run-lint
       - stackviz-nodejs10-run-test-browser
       - tempest-full-py3: