Issue #28076: Variable annotations should be mangled for private names.

By Ivan Levkivskyi.
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 914aa67..67a61d4 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -328,12 +328,12 @@
 
         # class semantics
         class C:
-            x: int
+            __foo: int
             s: str = "attr"
             z = 2
             def __init__(self, x):
                 self.x: int = x
-        self.assertEqual(C.__annotations__, {'x': int, 's': str})
+        self.assertEqual(C.__annotations__, {'_C__foo': int, 's': str})
         with self.assertRaises(NameError):
             class CBad:
                 no_such_name_defined.attr: int = 0