Make two PyModuleDef_Slot symbols static in _testmultiphase. (GH-8147)

Modules/_testmultiphase.c

@@ -236,7 +236,7 @@ static int execfunc(PyObject *m)
 
 #define TEST_MODULE_DEF(name, slots, methods) TEST_MODULE_DEF_EX(name, slots, methods, 0, NULL)
 
-PyModuleDef_Slot main_slots[] = {
+static PyModuleDef_Slot main_slots[] = {
     {Py_mod_exec, execfunc},
     {0, NULL},
 };
@@ -486,7 +486,7 @@ createfunc_null(PyObject *spec, PyModuleDef *def)
     return NULL;
 }
 
-PyModuleDef_Slot slots_create_null[] = {
+static PyModuleDef_Slot slots_create_null[] = {
     {Py_mod_create, createfunc_null},
     {0, NULL},
 };