Reference leak in code object with reference loop

If the code object creates a reference loop, this causes a reference leak. For example (see :

def f():
    return 1234.5

code = f.__code__
a = []
code = code.replace(co_consts=code.co_consts + (a,))
a.append(code)

(See https://github.com/python/cpython/blob/d61fcf834d197f0113a6a507fdbecc1545d9d483/Lib/test/test_marshal.py#L354-L360 added in #148698)

This is because in the GIL-enabled build the code object does not support GC and does not have tp_traverse.

Linked PRs

• gh-151155

從 Lib/test/test_marshal.py 中約第 354-360 行的重現程式碼和所引用的回歸測試開始。檢查啟用 GIL 的程式碼物件如何處理垃圾回收和走訪，重點關注 issue 中描述的缺少支援。完成的標準是參照迴圈不再洩漏，且 marshal 測試繼續通過。