flaky `test_traceback` on free-threaded Windows (x86)

[picnixz]

Bug report

Bug description:

ERROR: test_traceback (test.test_multiprocessing_spawn.test_processes.WithProcessesTestPool.test_traceback)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 2974, in test_traceback
    with self.Pool(1) as p:
         ~~~~~~~~~^^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\pool.py", line 739, in __exit__
    self.terminate()
    ~~~~~~~~~~~~~~^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\pool.py", line 657, in terminate
    self._terminate()
    ~~~~~~~~~~~~~~~^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\util.py", line 216, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "D:\a\cpython\cpython\Lib\multiprocessing\pool.py", line 690, in _terminate_pool
    change_notifier.put(None)
    ~~~~~~~~~~~~~~~~~~~^^^^^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\queues.py", line 394, in put
    self._writer.send_bytes(obj)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\connection.py", line 206, in send_bytes
    self._send_bytes(m[offset:offset + size])
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\multiprocessing\connection.py", line 293, in _send_bytes
    raise ValueError("concurrent send_bytes() calls "
                     "are not supported")
ValueError: concurrent send_bytes() calls are not supported

See https://github.com/python/cpython/actions/runs/14042338382/job/39315255511 (note that those changes are just removing casts so this shouldn't affect the test)

cc @colesbury

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

[colesbury]

This is not free threading specific

[colesbury]

This is the same underlying issue and stacktrace as #130733 so let's track them in a single issue.