Upgrade assistant changed unit test project from net6.0-windows to net9.0 causing issues with dependent projects

[mobiletonster]

I have a solution with 4 projects.

Application	Current Version	Post-Upgrade Version
app.server (ASP.NET Core Server)	net6.0	net9.0
app.shared (.NET class library)	net6.0	net9.0
app.client (WPF Desktop app)	net6.0-windows	net9.0-windows
app.test (windows test app)	net6.0-windows	**net9.0 **

Currently the .test project targets net6.0-windows because it has a reference to the .client (WPF) project and has units test that test the windows desktop application.

When I run the upgrader, it changes the WPF client project appropriately from net6.0-windows to net9.0-windows, however it changes the .test project from .net6.0-windows to just .net9.0. This breaks as a net9.0 project cannot reference another project that is a net9.0-windows project.

The upgrade-assistant should be more aware when upgrading the test project and preserve the -windows state when migrating to the new target.