switch documentation job to new PTI
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: I9c9f04fa42f89054ee1eeae1904fd08d30f98005
Story: #2002586
Task: #24314

openstack/networking-bgpvpn,openstack/networking-bgpvpn,openstack/networking-bgpvpn