``test_functools`` sometimes leaks references

The text below is a part of the refleak tests, and unfortunately, I am unable to constantly reproduce it :(

0:13:26 load avg: 7.84 [201/478/1] test_functools failed (reference leak) -- running (3): test.test_multiprocessing_spawn.test_processes (7 min 14 sec), test_embed (1 min 12 sec), test_faulthandler (55.3 sec)
beginning 6 repetitions. Showing number of leaks (. for 0 or less, X for 10 or more)
123:456
XX1 111

从 CPython 针对 test_functools 的 refleak 测试输出开始，并尝试在 refleak runner 下反复运行该测试。该报告是间歇性的，且未提供源文件或 reproducer，因此首先要隔离出哪个测试路径会泄漏引用。完成标准是确定发生泄漏的路径，并添加一个能够防止该泄漏的 regression fix 或测试。