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

从 Lib/test/test_marshal.py 中约第 354-360 行的复现代码和所引用的回归测试开始。检查启用 GIL 的代码对象如何处理垃圾回收和遍历，重点关注 issue 中描述的缺失支持。完成的标准是引用循环不再泄漏，并且 marshal 测试继续通过。