bpo-43908: Apply Py_TPFLAGS_IMMUTABLETYPE to array.array

Author: Erlend E. Aasland

Modules/arraymodule.c

@@ -2847,7 +2847,8 @@ static PyType_Slot array_slots[] = {
 static PyType_Spec array_spec = {
     .name = "array.array",
     .basicsize = sizeof(arrayobject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+              Py_TPFLAGS_IMMUTABLETYPE),
     .slots = array_slots,
 };