tests: Don't run tkpanels.Placer test without Tk already inited

Necessary for being able to run test suite on macOS

tests/tkpanels/test_Placer.py

@@ -4,7 +4,7 @@ from direct.showbase.ShowBase import ShowBase
 from direct.tkpanels.Placer import Placer
 
 
-def test_Placer(window):
+def test_Placer(window, tk_toplevel):
     base = ShowBase()
     base.start_direct()
     root = Pmw.initialise()