Replace Py_NotImplemented returns with the macro form Py_RETURN_NOTIMPLEMENTED.
The macro was introduced in #12724.
diff --git a/Objects/abstract.c b/Objects/abstract.c
index f992573..8298fd4 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -793,8 +793,7 @@
             return x;
         Py_DECREF(x); /* can't do it */
     }
-    Py_INCREF(Py_NotImplemented);
-    return Py_NotImplemented;
+    Py_RETURN_NOTIMPLEMENTED;
 }
 
 static PyObject *