idlelib tests: Fix refleak testing of test_zzdummy

Create a fresh test config for each test run.

Author: zware

Lib/idlelib/idle_test/test_zzdummy.py

@@ -11,7 +11,8 @@
 
 
 usercfg = zzdummy.idleConf.userCfg
-testcfg = {
+
+make_testcfg = lambda: {
     'main': config.IdleUserConfParser(''),
     'highlight': config.IdleUserConfParser(''),
     'keys': config.IdleUserConfParser(''),
@@ -128,7 +129,7 @@ def setUpClass(cls):
         root.withdraw()
         text = cls.text = Text(cls.root)
         cls.editor = DummyEditwin(root, text)
-        zzdummy.idleConf.userCfg = testcfg
+        zzdummy.idleConf.userCfg = make_testcfg()
 
     @classmethod
     def tearDownClass(cls):