Queue frozen objects for decref.

Author: ZeroIntensity

Python/gc_free_threading.c

@@ -906,7 +906,11 @@ gc_visit_thread_stacks_mark_alive(PyInterpreterState *interp, gc_mark_args_t *ar
 static void
 queue_untracked_obj_decref(PyObject *op, struct collection_state *state)
 {
-    if (!_PyObject_GC_IS_TRACKED(op)) {
+    assert(Py_REFCNT(op) == 0);
+    // We have to treat frozen objects as untracked in this function or else
+    // they might be picked up in a future collection, which breaks the assumption
+    // that all incoming objects have a non-zero reference count.
+    if (!_PyObject_GC_IS_TRACKED(op) || gc_is_frozen(op)) {
         // GC objects with zero refcount are handled subsequently by the
         // GC as if they were cyclic trash, but we have to handle dead
         // non-GC objects here. Add one to the refcount so that we can