doc:it_IT: fix typo in email-client

`usato` becomes `usando`

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Link: https://lore.kernel.org/r/20221230172456.58745-1-federico.vaga@vaga.pv.it


Signed-off-by: Jonathan Corbet <corbet@lwn.net>