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: I15c2d1da21c05c6530e7c05e8e90c2660a041144
Story: #2002586
Task: #24297

.zuul.yaml

@@ -125,8 +125,8 @@
     templates:
       - openstack-python-jobs
       - openstack-python35-jobs
-      - release-notes-jobs
-      - publish-openstack-sphinx-docs
+      - release-notes-jobs-python3
+      - publish-openstack-docs-pti
       - check-requirements
       - lib-forward-testing
     check: