`ToastNotificationManager.CreateToastNotifier()` crash the app if user change their username without signing out

Nobody has claimed this yet.

### Describe the bug

My app recently get a user report of crashing. After checking the log, I found it crashes in toast notification related apis. His pc was connected to a domain, and has its username changed, without manual rebooting / manual signing out his account. Some quick experiment found out that if you launch the app first then change your username, calling `ToastNotificationManager.CreateToastNotifier()` will throw exception.

This is very corner case, but I think it should be documented (or don't throw exception). The majority of the WinRT api can still function normally in this case.

### Steps to reproduce the bug

1. Create a winui3 C++ app packaged
2. Use this code:
```cpp
void MainWindow::myButton_Click(IInspectable const&, RoutedEventArgs const&)
{
myButton().Content(box_value(L"Clicked"));

winrt::Windows::Data::Xml::Dom::XmlDocument doc;
doc.LoadXml(LR"(



Hello World
This is a simple toast message



)");
winrt::Windows::UI::Notifications::ToastNotification toast{ doc };

winrt::Windows::UI::Notifications::ToastNotificationManager::CreateToastNotifier()
.Show(toast);

MessageBox(NULL, L"", L"finished", 0);
}
```
3. Build and run the app
4. Change the username (you can simply run `netplwiz` to do that)
5. Click the button to send a toast, observe the crash

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

Windows App SDK 1.6.3: 1.6.241114003

### Packaging type

Packaged (MSIX)

### Windows version

_No response_

### IDE

Visual Studio 2022

### Additional context

Windows 11 23H2

Reproduce the crash in a packaged WinUI 3 C++ app using ToastNotificationManager::CreateToastNotifier(), following the provided username-change steps on Windows 11 23H2. Investigate whether the behavior should be documented or changed so the call does not throw an exception; completion would require one of those outcomes to be established.

Written by the indexing model from the issue text.