Fix a bug in Generic.__new__ (GH-6758)

Author: ilevkivskyi

Lib/test/test_typing.py

@@ -1367,6 +1367,9 @@ def test_new_no_args(self):
         class A(Generic[T]):
             pass
 
+        with self.assertRaises(TypeError):
+            A('foo')
+
         class B:
             def __new__(cls):
                 # call object

Lib/typing.py

@@ -836,7 +836,7 @@ def __new__(cls, *args, **kwds):
         if cls is Generic:
             raise TypeError("Type Generic cannot be instantiated; "
                             "it can be used only as a base class")
-        if super().__new__ is object.__new__:
+        if super().__new__ is object.__new__ and cls.__init__ is not object.__init__:
             obj = super().__new__(cls)
         else:
             obj = super().__new__(cls, *args, **kwds)