Update Environment.xml

[birken25]

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

[mairaw]

@carlossanlop can you help find the area owner?

[carlossanlop]

@mairaw I don't think this area has a specific owner, but the code is pretty straightforward:

https://github.com/dotnet/runtime/blob/2c6ec170197f42ce5ce21ceca27e89af6f1e6030/src/libraries/System.Private.CoreLib/src/System/Environment.Win32.cs#L118-L168

The UserName property calls the internal method GetUserName, which in turn does a P/Invoke to the Windows method GetUserNameExW, which has a very similar description in the official documentation, particularly regarding the current thread's user:

https://docs.microsoft.com/en-us/windows/win32/api/secext/nf-secext-getusernameexw

Retrieves the name of the user or other security principal associated with the calling thread. You can specify the format of the returned name.

[mairaw]

Sounds good @carlossanlop! Thank you @birken25. Your contribution will show up live within a day or so.