doc: fix asyncLocalStorage.run() description

The description that store is not available
when asynchronous operation is created within
the callback is not accurate

PR-URL: https://github.com/nodejs/node/pull/40381


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>