Fix test_typing.test_readonly_inheritance

Backport of python/cpython#128618

Author: sobolevn

src/test_typing_extensions.py

@@ -4624,13 +4624,13 @@ class Child1(Base1):
         self.assertEqual(Child1.__mutable_keys__, frozenset({'b'}))
 
         class Base2(TypedDict):
-            a: ReadOnly[int]
+            a: int
 
         class Child2(Base2):
-            b: str
+            b: ReadOnly[str]
 
-        self.assertEqual(Child1.__readonly_keys__, frozenset({'a'}))
-        self.assertEqual(Child1.__mutable_keys__, frozenset({'b'}))
+        self.assertEqual(Child2.__readonly_keys__, frozenset({'b'}))
+        self.assertEqual(Child2.__mutable_keys__, frozenset({'a'}))
 
     def test_make_mutable_key_readonly(self):
         class Base(TypedDict):