[3.12 Regression] backport of gh-120233 to 3.12 (gh-121350) breaks mercurial, working with 3.12.4

Bug report

Bug description:

mercurial 6.8 fails to start with the 3.12 branch 2024-07-15, but works with 3.12.4:

~$ hg
Traceback (most recent call last):
File "/usr/bin/hg", line 57, in
from mercurial import dispatch
File "", line 1360, in _find_and_load
File "", line 1331, in _find_and_load_unlocked
File "", line 935, in _load_unlocked
File "/usr/lib/python3/dist-packages/hgdemandimport/demandimportpy3.py", line 52, in exec_module
super().exec_module(module)
File "", line 257, in exec_module
File "", line 1360, in _find_and_load
File "", line 1331, in _find_and_load_unlocked
File "", line 935, in _load_unlocked
File "/usr/lib/python3/dist-packages/hgdemandimport/demandimportpy3.py", line 52, in exec_module
super().exec_module(module)
File "", line 267, in exec_module
AttributeError: partially initialized module 'threading' has no attribute 'RLock' (most likely due to a circular import)

Commenting out the hgdemandimport.enable() at line 55 of /usr/bin/hg, it works:

Complete bug report at https://bugs.debian.org/1076449

CPython versions tested on:

3.12

Operating systems tested on:

Linux

报告指出了第 55 行的 /usr/bin/hg 和 hgdemandimport.enable()，并以 Debian 错误报告作为补充背景。首先在 3.12 分支上相对于 3.12.4 重现 mercurial 6.8 的启动失败，并检查 gh-120233/gh-121350 回归；当 hg 能够在没有 threading 循环导入错误的情况下启动时，即视为完成。