Avoid configuring DI for ILogger<T> in tests

In some test code we are creating a host application builder and instantiating serilog to do app logging.

https://github.com/coder/coder-desktop-windows/blob/a6f7bb67bb111628d3de1f46d7b404d4bab67717/App/Services/MutagenController.cs#L160-L162

We should probably just write an implementation for `ILogger` and `ILogger` that log to the test output. It can use serilog under the hood if that makes it easier.

IDK where we'd put it, though. Maybe we should add add a `Test.Utils` project or something