Bug with unwatching

Hello!

Testing your code:

```julia
using BetterFileWatching

watch_task = @async watch_folder(".") do event
    @info "Something changed!" event
    @info typeof(event)
end

sleep(5)

# stop watching the folder
schedule(watch_task, InterruptException(); error=true)
```

After the task is done, it keeps registering changes unfortunately in the folder. How to fix?

Kind regards