Determine which async worker in `Host::try_init` is failing to drop the `Lockfile` when `try_init` is cancelled

[gefjon]

Follow-up from #2857 . Some async task spawned by Host::try_init is keeping a handle on the Lockfile alive longer than it should, making Host::try_init not cancel-safe. Find out what task that is, and make it so that it drops the Lockfile immediately when try_init is cancelled, or the database is otherwise shut down.