Fix tautological-compare in cinderx/ParallelGC/parallel_gc.c +1

Summary:
LLVM has a warning `-Wtautological-compare` which gets triggered when overlapping comparisons create a statement that is always true or always false. Such a comparison occurred in this code and, here, I try to fix it.

Please review carefully!

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Reviewed By: alexmalyshev

Differential Revision: D92525751

fbshipit-source-id: da4b234f8bc2ce1677c1a84694d084a13c90e6a8

Author: r-barnes

cinderx/ParallelGC/parallel_gc.c

@@ -358,7 +358,7 @@ static void validate_list(PyGC_Head* head, enum flagstates flags) {
       next_value = NEXT_MASK_UNREACHABLE;
       break;
     default:
-      assert(!"bad internal flags argument");
+      assert(0 && "bad internal flags argument");
   }
   PyGC_Head* prev = head;
   PyGC_Head* gc = GC_NEXT(head);