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: I0b373b18715fec1bed6894bb324d104fb78893e6
Story: #2002586
Task: #24327

.zuul.yaml

@@ -2,7 +2,7 @@
     templates:
       - nodejs4-jobs
       - openstack-python-jobs
-      - publish-openstack-sphinx-docs
+      - publish-openstack-docs-pti
       - openstack-python35-jobs
     periodic:
       jobs: