test_typing: use all pickle protocols (GH-99154)

(cherry picked from commit a0bc75e)

Co-authored-by: Nikita Sobolev <[email protected]>

Author: miss-islington

Lib/test/test_typing.py

@@ -2896,7 +2896,7 @@ class CP(P[int]):
             self.assertEqual(x.bar, 'abc')
             self.assertEqual(x.x, 1)
             self.assertEqual(x.__dict__, {'foo': 42, 'bar': 'abc'})
-            s = pickle.dumps(P)
+            s = pickle.dumps(P, proto)
             D = pickle.loads(s)
 
             class E: