Replace Py_NotImplemented returns with the macro form Py_RETURN_NOTIMPLEMENTED.
The macro was introduced in #12724.
diff --git a/Objects/memoryobject.c b/Objects/memoryobject.c
index 2e32b2a..e0d1a89 100644
--- a/Objects/memoryobject.c
+++ b/Objects/memoryobject.c
@@ -773,8 +773,7 @@
 _notimpl:
     PyBuffer_Release(&vv);
     PyBuffer_Release(&ww);
-    Py_INCREF(Py_NotImplemented);
-    return Py_NotImplemented;
+    Py_RETURN_NOTIMPLEMENTED;
 }