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: I42d7f8bbba2e88d7236bd1032d11ebfa8deab2d7
Story: #2002586
Task: #24286

.zuul.yaml

@@ -3,8 +3,8 @@
       - openstack-python-jobs-horizon
       - check-requirements
       - openstack-python35-jobs-horizon
-      - release-notes-jobs
-      - publish-openstack-sphinx-docs
+      - release-notes-jobs-python3
+      - publish-openstack-docs-pti
     check:
       jobs:
         - openstack-tox-lower-constraints: