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: I2e313bb43d3a03a0d516cd87a77b3911363de7ee
Story: #2002586
Task: #24305

zuul.d/project.yaml

@@ -4,8 +4,8 @@
       - openstack-python-jobs
       - openstack-python35-jobs
       - check-requirements
-      - publish-openstack-sphinx-docs
+      - publish-openstack-docs-pti
-      - release-notes-jobs
+      - release-notes-jobs-python3
       - deploy-guide-jobs
     check:
       jobs: