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: Ia419cdf086bc30715fd6e984d8c40e194c9eaae4
Story: #2002586
Task: #24341

zuul.d/layout.yaml

@@ -1,7 +1,7 @@
 - project:
     templates:
       - check-requirements
-      - release-notes-jobs
+      - release-notes-jobs-python3
     check:
       jobs:
         - tripleo-ci-centos-7-scenario000-multinode-oooq-container-updates