doc: fix introduced_in note in querystring.md

The method descriptions mentioned the right version but for some reason
the top-level description did not. Well, now it does.

PR-URL: https://github.com/nodejs/node/pull/29014


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>