Use multi-phase initialization

src/_jpegxl.c

@@ -616,22 +616,22 @@ setup_module(PyObject *m) {
     return 0;
 }
 
+static PyModuleDef_Slot slots[] = {
+    {Py_mod_exec, setup_module},
+#ifdef Py_GIL_DISABLED
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+#endif
+    {0, NULL}
+};
+
 PyMODINIT_FUNC
 PyInit__jpegxl(void) {
-    PyObject *m;
-
     static PyModuleDef module_def = {
         PyModuleDef_HEAD_INIT,
         .m_name = "_jpegxl",
-        .m_size = -1,
         .m_methods = jpegxlMethods,
+        .m_slots = slots
     };
 
-    m = PyModule_Create(&module_def);
+    return PyModuleDef_Init(&module_def);
-    if (setup_module(m) < 0) {
-        Py_DECREF(m);
-        return NULL;
-    }
-
-    return m;
 }