Python 3.8 deprecation warning from cryptography

[victorlin]

The following warning started appearing a couple days ago, first seen in scheduled CI run:

cryptography.utils.CryptographyDeprecationWarning: Python 3.8 is no longer supported by the Python core team and support for it is deprecated in cryptography. The next release of cryptography will remove support for Python 3.8.

This is due to pyca/cryptography@595f6de released in version 47.0.0.

It causes pytest to fail because the warning is emitted as an unmatched exception in doctests.

Short-term solution

• Suppress warning from cryptography about deprecated Python 3.8 support #523

Long-term solution

• Drop support for Python 3.8
  • I have a draft for this on branch victorlin/update-python-versions

[joverlee521]

I can add the short term warning suppression.