Test failures in `_compat_test.py/test_deprecated_module`

[maffoo]

I'm seeing failures in CI in _compat_test.py/test_deprecated_module: https://github.com/quantumlib/Cirq/actions/runs/7097897242/job/19318827306?pr=6372. The tests are not seeing expected log messages from a deprecation.

[maffoo]

I was initially unable to reproduce this locally, but when I updated my local virtualenv with

pip install --upgrade -r dev_tools/requirements.dev.env.txt

I was able to reproduce the failures. So it seems likely that a new version of a dependency is interacting in some way with multiprocessing and causing this problem, but I haven't narrowed down which dependency it is. After upgrading with the above command you can reproduce the problem with

pytest cirq-core/cirq/testing/ cirq-core/cirq/_compat_test.py