Obscure error message when modifying property accessed by UI on timer thread

Nobody has claimed this yet.

### Describe the bug

Normally, when you access anything that the UI concerns from another thread, you have to go through the dispatcher. A member in the UWP Community Discord ran into this same problem, but was met with a very undescriptive error message, saying `System.Runtime.InteropServices.COMException: ""`.

Though, I do recall seeing the proper error message before when this happened, but I don't remember how long ago that was.

### Steps to reproduce the bug

https://github.com/Pdawg-bytes/WASDK-INPC-COMException-repro/tree/main
Clone this repository and run the app. Take note of the comments in `App1/SystemViewModel.cs`.

### Expected behavior

When you attempt to access something like this, the error message should tell you that you need to use the Dispatcher to dispatch it to the UI thread.

### Screenshots

Here's the undescriptive error message:

### NuGet package version

WinUI 3 - Windows App SDK 1.6.0: 1.6.240829007

### Windows version

Windows 11 (22H2): Build 22621

### Additional context

_No response_

Clone and run the linked WASDK-INPC-COMException-repro app, starting with the comments in App1/SystemViewModel.cs. Reproduce the timer-thread property access and trace where the empty COMException is surfaced; done means the failure provides the expected guidance to dispatch access to the UI thread.

Written by the indexing model from the issue text.