doc: fix socket.connecting description

In particular, this value is `true` and not `false`
between calling `connect()` and the operation finishing.

PR-URL: https://github.com/nodejs/node/pull/24066


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>