Test test_pool.test_on_ready_counter_is_synchronized may fail if the CPU is under heavy load

[FliegendeWurst]

I am trying to execute the tests on version 4.2.1, but I get the error below if I run a lot of other CPU-intensive work in the background.
(the tests all pass if I pause my background processes)

============================= test session starts ==============================
platform linux -- Python 3.12.7, pytest-8.3.3, pluggy-1.5.0
rootdir: /build/source
configfile: setup.cfg
testpaths: t/unit/
collected 81 items

t/unit/test_common.py ........                                           [  9%]
t/unit/test_dummy.py .                                                   [ 11%]
t/unit/test_einfo.py .........                                           [ 22%]
t/unit/test_package.py .                                                 [ 23%]
t/unit/test_pool.py ...F                                                 [ 28%]
t/unit/test_spawn.py ...                                                 [ 32%]
t/unit/test_values.py ....                                               [ 37%]
t/unit/test_win32.py sssssssssssssssssssssssssssssssssssssssssssssssssss [100%]

=================================== FAILURES ===================================
_______________ test_pool.test_on_ready_counter_is_synchronized ________________

self = <t.unit.test_pool.test_pool object at 0x7ffff5bfa810>

    def test_on_ready_counter_is_synchronized(self):
        for ctx in ('spawn', 'fork', 'forkserver'):
            pool = billiard.pool.Pool(processes=1, context=get_context(ctx))
>           pool.apply_async(func, (1,)).get(1)

t/unit/test_pool.py:53:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <ApplyResult: 7 ack:False ready:False>, timeout = 1

    def get(self, timeout=None):
        self.wait(timeout)
        if not self.ready():
>           raise TimeoutError
E           multiprocessing.context.TimeoutError

billiard/pool.py:1785: TimeoutError
=============================== warnings summary ===============================
t/unit/test_pool.py::test_pool::test_exception_traceback_present
t/unit/test_spawn.py::test_spawn::test_set_pdeathsig
t/unit/test_values.py::test_values::test_value
t/unit/test_values.py::test_values::test_rawvalue
  /build/source/billiard/popen_fork.py:70: DeprecationWarning: This process (pid=232) is multi-threaded, use of fork() may lead to deadlocks in the child.
    self.pid = os.fork()

t/unit/test_spawn.py::test_spawn::test_start
  /nix/store/7xi8n243nis25ql9q5hmpjj5zp2p0ygb-python3.12-pytest-8.3.3/lib/python3.12/site-packages/_pytest/python.py:163: PytestReturnNotNoneWarning: Expected None, but t/unit/test_spawn.py::test_spawn::test_start returned 0, which will be an erro
r in a future version of pytest.  Did you mean to use `assert` instead of `return`?
    warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================== short test summary info ============================
FAILED t/unit/test_pool.py::test_pool::test_on_ready_counter_is_synchronized - multiprocessing.context.TimeoutError
============= 1 failed, 29 passed, 51 skipped, 5 warnings in 9.35s =============

See NixOS/nixpkgs#357170 for more details.