Fix Python 3.10 (PEP-620) incompatibility.

src/object/function.cpp

@@ -107,7 +107,7 @@ function::function(
     PyObject* p = this;
     if (Py_TYPE(&function_type) == 0)
     {
-        Py_TYPE(&function_type) = &PyType_Type;
+        Py_SET_TYPE(&function_type, &PyType_Type);
         ::PyType_Ready(&function_type);
     }