gh-121390: tracemalloc: Fix tracebacks memory leak (#121391)

The tracemalloc_tracebacks hash table has traceback keys and NULL
values, but its destructors do not reflect this -- key_destroy_func is
NULL while value_destroy_func is raw_free. Swap these to free the
traceback keys instead.

Python/tracemalloc.c

@@ -838,7 +838,7 @@ _PyTraceMalloc_Init(void)
 
     tracemalloc_tracebacks = hashtable_new(hashtable_hash_traceback,
                                            hashtable_compare_traceback,
-                                           NULL, raw_free);
+                                           raw_free, NULL);
 
     tracemalloc_traces = tracemalloc_create_traces_table();
     tracemalloc_domains = tracemalloc_create_domains_table();