pythongh-117657: Quiet TSAN warning about a data race between `start_…

…the_world()` and `tstate_try_attach()` (python#117828)

TSAN erroneously reports a data race between the `_Py_atomic_compare_exchange_int`
on `tstate->state` in `tstate_try_attach()` and the non-atomic load of
`tstate->state` in `start_the_world`. The `_Py_atomic_compare_exchange_int` fails,
but TSAN erroneously treats it as a store.

Python/pystate.c

@@ -2248,7 +2248,8 @@ start_the_world(struct _stoptheworld_state *stw)
     PyThreadState *t;
     _Py_FOR_EACH_THREAD(stw, i, t) {
         if (t != stw->requester) {
-            assert(t->state == _Py_THREAD_SUSPENDED);
+            assert(_Py_atomic_load_int_relaxed(&t->state) ==
+                   _Py_THREAD_SUSPENDED);
             _Py_atomic_store_int(&t->state, _Py_THREAD_DETACHED);
             _PyParkingLot_UnparkAll(&t->state);
         }