CVE-2025-64708: authentik's invitation expiry is delayed by at least 5 minutes

In previous authentik versions, invitations were considered valid regardless if they are expired or not, thus relying on background tasks to clean up expired ones. In a normal scenario this can take up to 5 minutes because the cleanup of expired objects is scheduled to run every 5 minutes. However, with a large amount of tasks in the backlog, this might take longer.