Fix GOA accounts throwing an error when starting offline

Don't check service credentials are loaded when the account is being
opened, since GOA accounts will do a
org.gnome.OnlineAccounts.Account::EnsureCredentials() call, and this
will error out if the creds are invalid or not available.

Instead, check when we know that the services should be reachable, and
hope that means the GOA provider's auth service is reachable, too.
5 jobs for wip/goa-error-when-disconnected in 24 minutes and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #233573
fedora

00:12:34

passed #233574
ubuntu

00:17:56

 
  Test
passed #233575
flatpak

00:04:33

 
  Deploy
passed #233576
review

00:01:07

passed #233577
allowed to fail manual
stop_review

00:00:43