FluentTests sometime causes unit tests failures locally and in CI

[BDisp]

GuiTestContext call Application.Run, which we know that is singleton, inside a background thread. What's happening is that a previous still running app wasn't closed and disposed and a new call to Application.Run happen causing some failures, sometimes with the message "Application was hard stopped, typically this means it timed out or did not shutdown gracefully. Ensure you call Stop in your test" or System.NullReferenceException or "Index was outside the bounds of the array", etc... The two latest errors normally occurs in the layout process when the new app is starting with new objects when the previous layout is still running.