gh-128679: Clear the ref trace in _PyTraceMalloc_Stop()

_PyTraceMalloc_Stop() now calls PyRefTracer_SetTracer(NULL, NULL).

Author: vstinner

Python/tracemalloc.c

@@ -986,6 +986,8 @@ _PyTraceMalloc_Stop(void)
     raw_free(tracemalloc_traceback);
     tracemalloc_traceback = NULL;
 
+    (void)PyRefTracer_SetTracer(NULL, NULL);
+
 done:
     TABLES_UNLOCK();
 }