verify: skip tkinter tests when DISPLAY not set

Author: indygreg

src/verify_distribution.py

@@ -109,6 +109,7 @@ def test_ssl(self):
 
         ssl.create_default_context()
 
+    @unittest.skipIf("DISPLAY" not in os.environ, "DISPLAY not set")
     def test_tkinter(self):
         import tkinter as tk