[docs] [issue35042] Use the role :pep: for the PEP \d+

[Stéphane Wirtel]

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


----------
keywords: +patch
pull_requests: +9374
stage:  -> patch review

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35042>
_______________________________________