Hang when using SMTP with `EagerBroker`

Using the default worker count of 1 leads to hangs when using SMTP, as send_group_invitation_mail at canaille/core/endpoints/groups.py:285 will trigger LOGO generation in canaille/app/mails.py:28, which by default will attempt to fetch from itself. When using dramatiq_eager_broker:EagerBroker this will wait forever.

The urllib.urlopen should have a timeout added, for example timeout=5. To avoid a restart being necessary, this might be relevant for more places as well.

Setting the workers up (CANAILLE_HYPERCORN__WORKERS=2 ) does not seem to help the behavior, but instead makes it erratic.

Only workaround I have found is to set LOGO = "" to avoid this circular loop. But this is not a perfect solution.