keyring >=24.0.0 on macos somehow corrupts multiprocessing

[Roguelazer]

Describe the bug
This is one of the weirder bugs that I've ever run into. If you use the keyring module to read a credential on macOS and then subsequently close a multiprocessing.ThreadPool instance during interpreter shutdown, the multiprocessing module crashes.

To Reproduce

Run the following script:

import keyring
# this is load-bearing: if you don't import multiprocessing first, everything works. some kind
# of reference-counting issue?
import multiprocessing
from multiprocessing.pool import ThreadPool

class Repro:
    def __init__(self):
        self.pool = ThreadPool()

    def __del__(self):
        if self.pool is not None:
            self.pool.close()
            self.pool.join()
            self.pool = None


def main():
    # comment out the call to keyring, and everything's fine
    keyring.get_password("example", "example-credential")
    # this needs to be bound to a variable so that __del__ runs at shutdown; if you just do
    # Repro(token), the destructor runs immediately and it doesn't exhibit the bug
    client = Repro()


main()

Expected behavior
The program should not print a traceback or crash

Actual behavior
The program reliably prints a warning like

Exception ignored in: <function Repro.__del__ at 0x1059fa520>
Traceback (most recent call last):
  File "./test_mp.py", line 13, in __del__
  File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/pool.py", line 652, in close
  File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/queues.py", line 371, in put
AttributeError: 'NoneType' object has no attribute 'dumps'

Environment

• OS: macOS
• Python Version: Tested 3.11, 3.12, and 31.3

./venv311/bin/pip list | grep keyring
keyring            25.6.0
$ ./venv311/bin/keyring --list-backends
keyring.backends.fail.Keyring (priority: 0)
keyring.backends.macOS.Keyring (priority: 5)
keyring.backends.chainer.ChainerBackend (priority: -1)

Additional context
I tested with various keyring versions and this was introduced in 24.0.0; version 23.13.1 does not exhibit the problem.

I read the diff between them and... nothing jumps out to me...