CI tests failing due to new version of flake8

[ich199]

A new version (6.1.0) of flake8 was released 2 weeks ago (29 July 2023) and seems to be causing the flake8 CI check to fail for existing tests:

$ pip list
Package     Version
----------- -------
flake8      6.1.0
mccabe      0.7.0
pip         23.2.1
pycodestyle 2.11.0
pyflakes    3.1.0
setuptools  62.6.0

$ flake8 .  
./tests/test_crypto.py:1745:16: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
./tests/test_crypto.py:3153:16: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
./tests/test_crypto.py:3448:16: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
./tests/test_crypto.py:3449:16: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
./tests/test_ssl.py:194:8: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`

$ echo $?
1

The previous version (6.0.0) used by the CI check passes:

$ pip list
Package     Version
----------- -------
flake8      6.0.0
mccabe      0.7.0
pip         23.2.1
pycodestyle 2.10.0
pyflakes    3.0.1
setuptools  62.6.0

$ flake8 .

$ echo $?
0

CI job from 2 weeks ago: https://github.com/pyca/pyopenssl/actions/runs/5701250353/job/15451784196#step:5:22

vs

current CI job: https://github.com/pyca/pyopenssl/actions/runs/5822365531/job/15786833735?pr=1239#step:5:22