Unable to start Qt app if non-ASCII character in path

### Describe the bug

Hi,

Windows App create with PySide6 are unable to start if a non ASCII character is set in the application path.
I had the case with a per-user installation and my %USERNAME% contain a "ë". Qt is unable to found his resources with an error message "Application failed to start because no Qt platform plugin could be initialized".
I have no problem with per-system installation.

### Steps to reproduce

1. Create a Windows App with PySide6
2. Install the app on a path with non ASCII character
3. Try to start the app

### Expected behavior

Be able to start the app without errors

### Screenshots


### Environment

- Operating System: Windows 11 22H2
- Python version: Python 3.11.2
- Software versions:
- Briefcase: 0.3.12
- PySide6: 6.4.2

### Logs

```
Log started: 2023-03-08 14:17:30Z
PreInitializing Python runtime...
PythonHome: C:\Users\usernameWithë\AppData\Local\Programs\devname\Autotype
PYTHONPATH:
- C:\Users\usernameWithë\AppData\Local\Programs\devname\Autotype\python311.zip
- C:\Users\usernameWithë\AppData\Local\Programs\devname\Autotype\Autotype
- C:\Users\usernameWithë\AppData\Local\Programs\devname\Autotype\app_packages
- C:\Users\usernameWithë\AppData\Local\Programs\devname\Autotype\app
Configure argc/argv...
Initializing Python runtime...
Running app module: autotype
---------------------------------------------------------------------------

```

### Additional context

After research and debug, I'm not sure if the problem came from the Stub.exe or from PySide.
It's a professional computer link to an AD. I didn't choose the %USERNAME%.

Start by reproducing the Windows 11 per-user installation with a non-ASCII username or install path, using the Briefcase 0.3.12 and PySide6 6.4.2 setup described in the issue. Use the startup log to investigate whether resource resolution fails in Stub.exe or PySide6. Done means the packaged app starts successfully from a path containing non-ASCII characters.

Written by the indexing model from the issue text.