doc: fix the inline code-block at the NodeDhKeyGenParams class

PR-URL: https://github.com/nodejs/node/pull/40341


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Qingyu Deng <i@ayase-lab.com>