Fix unused classes in test case (#122)

Author: JosephSBoyle

src/test_typing_extensions.py

@@ -1859,8 +1859,8 @@ def __init__(self):
         class DI:
             def __init__(self):
                 self.x = None
-        self.assertIsInstance(C(), P)
-        self.assertIsInstance(D(), P)
+        self.assertIsInstance(CI(), P)
+        self.assertIsInstance(DI(), P)
 
     def test_protocols_in_unions(self):
         class P(Protocol):