AppInstance.FindOrRegisterForKey throws ArgumentException: The parameter is incorrect

### Describe the bug

While trying to track down crashes, I put `var keyInstance = AppInstance.FindOrRegisterForKey("main"); ` in a try-catch and found that it's throwing an `ArgumentException` (with message "`The parameter is incorrect.\r\n\r\nThe parameter is incorrect`") for some of my users.

### Steps to reproduce the bug

```
class Program
{
[STAThread]
static void Main()
{
try
{
var keyInstance = AppInstance.FindOrRegisterForKey("main");
if (keyInstance.IsCurrent)
{
keyInstance.Activated += (_, _) => App.HandleAppActivation();
Application.Start(p =>
{
var context = new DispatcherQueueSynchronizationContext(DispatcherQueue.GetForCurrentThread());
SynchronizationContext.SetSynchronizationContext(context);
_ = new App();
});
}
else { keyInstance.RedirectActivationToAsync(AppInstance.GetCurrent().GetActivatedEventArgs()).GetAwaiter().GetResult(); }
}
catch (Exception ex) { **log error** }
}
}
```

### Expected behavior

No exception

### Screenshots

_No response_

### NuGet package version

Windows App SDK 1.7.3: 1.7.250606001

### Packaging type

Packaged (MSIX)

### Windows version

Windows 11 version 24H2 LTSC (26100, June Update)

### IDE

Visual Studio 2022

### Additional context

_No response_

Start with the provided Program.Main reproduction and investigate AppInstance.FindOrRegisterForKey("main") using Windows App SDK 1.7.3 on Windows 11 24H2 LTSC. Compare the failing and expected paths, then verify that the call completes without the reported ArgumentException for the packaged MSIX scenario.

Written by the indexing model from the issue text.