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: I0d5c754e54910f3bdca69470dd518411a0958d83
Story: #2002586
Task: #24291

.zuul.yaml

@@ -2,7 +2,7 @@
     templates:
       - openstack-python-jobs
       - check-requirements
-      - release-notes-jobs
+      - release-notes-jobs-python3
       - publish-openstack-docs-pti
     check:
       jobs: