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: Ibfd7b4f7ed01e27cad9bfb9339a6db2487a40286
Story: #2002586
Task: #24293

.zuul.yaml

@@ -15,7 +15,7 @@
       - openstack-python35-jobs
       - openstack-python36-jobs
       - check-requirements
-      - publish-openstack-sphinx-docs
+      - publish-openstack-docs-pti
     check:
       jobs:
         - os-api-ref-nova-src