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: I65f28213bd98ab03751ab910cb5ce4626de8aabc

.zuul.yaml

@@ -8,6 +8,8 @@
         - openstack-tox-py37
         - openstack-tox-py38
         - openstack-tox-py39
+        - openstack-tox-py310:
+            voting: false
     gate:
       jobs:
         - openstack-tox-pep8