A recent change defaults the warning-as-error to True:
https://review.openstack.org/#/c/559348/
Which is causing our documentation jobs to fail locally and in the
gate/check queues.
This commit fixes both issues that are causing failures so that
we can get the doc jobs passing again.
Closes-Bug: 1774508
Change-Id: Ic1eff48a6f40aa315cc5e566a0f9e930a20b9837