doc: fix indentation on http2 doc entry

PR-URL: https://github.com/nodejs/node/pull/36869


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: Harshitha K P <harshitha014@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>