On Linux and macOS, no program output was being observed.
This is referenced in the [LocalTime] docs for `tracing-subscriber`,
which links to this [unsoundness issue] in the time crate.
Rather than introducing a possible vector for undefined behaviour and
segfaults, I have just changed the logging to use UTC time instead.
When running the ASB as a systemd service, one would generally use the
`--disable-timestamps` flag anyway as systemd adds its own timestamps
which can be local to the server.
If the situation with `tracing-subscriber` and the time crate is fixed
then this can be updated.
This commit also updates the `tracing-subscriber` and `tracing-appender`
dependencies, closing #987.
[LocalTime]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/time/struct.LocalTime.html
[unsoundness issue]: https://github.com/time-rs/time/issues/293#issuecomment-748151025
