doc: fix code display in header glitch

Fixes: https://github.com/nodejs/node/issues/31451

PR-URL: https://github.com/nodejs/node/pull/31460


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Geoffrey Booth <webmaster@geoffreybooth.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>