Launching Terminal Preview as an administrator causes the username environment variable to be "SYSTEM"

### Windows Terminal version

1.18.1462.0

### Windows build number

10.0.22621.0

### Other Software

_No response_

### Steps to reproduce

Right-click on WT icon and select "Run as Administrator"
Enter credentials for a different account than the signed in one.
When the pwsh prompt load, do '$env:username'
The result is "SYSTEM" instead of the expected username.

This does not occur when one launches pwsh outside of WT.

### Expected Behavior

Username returned by the 'username' environment variable should be the same as the credentials used to launch the application

### Actual Behavior

The 'username' environment variable returns "SYSTEM"

Reproduce the issue by launching Windows Terminal with “Run as Administrator,” entering different credentials, and checking $env:username in the pwsh prompt. Trace the administrator launch and environment propagation paths; done means the variable matches the credentials used to launch the application, as it does when pwsh is launched outside Windows Terminal.

Written by the indexing model from the issue text.