Only import tkinter when needed
Only import tkinter when needed

* Otherwise this could fail if tkinter isn't available on platforms where we're
  not even going to run the test

Zorro666/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,baldurk/renderdoc,baldurk/renderdoc