Fix unused classes in a typing test (GH-102437)

As part of investigation issue #102433, I discovered what I believe to be an error where two classes `CI` and `DI` are not being used. The assertions beneath them act on `C` and `D`, duplicating existing assertions in this test.
(cherry picked from commit 7894bbe)

Co-authored-by: JosephSBoyle <48555120+JosephSBoyle@users.noreply.github.com>
Automerge-Triggered-By: GH:AlexWaygood

Author: miss-islington

Lib/test/test_typing.py

@@ -1528,8 +1528,8 @@ 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):