[docs] [issue34839] doctest: Change example under warnings section

[Stéphane Wirtel]

Change by Stéphane Wirtel <stephane at wirtel.be>:


----------
keywords: +patch
pull_requests: +9123
stage: needs patch -> patch review

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34839>
_______________________________________