switch documentation job to new PTI

This is a mechanically generated patch to switch the documentation
jobs to use the new PTI versions of the jobs as part of the
python3-first goal.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: Iec120273145999da9b528dae7f2b66a4a3d1a330
Story: #2002586
Task: #24341

.zuul.yaml

@@ -1,9 +1,9 @@
 - project:
     templates:
-      - publish-openstack-sphinx-docs
+      - publish-openstack-docs-pti
     check:
       jobs:
-        - build-openstack-sphinx-docs
+        - openstack-tox-docs
     gate:
       jobs:
-        - build-openstack-sphinx-docs
+        - openstack-tox-docs