internal class TimedHostedService : IHostedService, IDisposable
{
    public TimedHostedService(IServiceProvider services)
    {
    }

    private async Task Test()
    {
        using (var scope = _services.CreateScope())
        {
            var mediator = scope.ServiceProvider.GetRequiredService<IMediator>();
            await mediator.Send(new Application.Test.Command());
        }
    }
}

internal class TimedHostedService : IHostedService, IDisposable
{
    ...

    public TimedHostedService(IServiceScopeFactory scopeFactory)
    {
    }

    private async Task Test()
    {
        using (var scope = _scopeFactory.CreateScope())
        {
            var mediator = scope.ServiceProvider.GetRequiredService<IMediator>();
            await mediator.Send(new Application.Test.Command());
        }
    }

    ...
}