Fix class definition.

Author: skv0zsneg

Lib/test/test_abc.py

@@ -735,7 +735,7 @@ class B(A, metaclass=abc_ABCMeta, name="test"):
 
     class TestAbstractClassErrorMessage(unittest.TestCase):
 
-        class MyAbstractClass(abc.ABC):
+        class MyAbstractClass(metaclass=abc_ABCMeta):
             @abc.abstractmethod
             def my_method(self):
                 pass