CI fails due to change in Python 3.6 deprecation warning from cryptography

[tsibley]

CI is failing (example) on test-source on 3.6 because of a Python 3.6 deprecation warning from cryptography:

E   cryptography.utils.CryptographyDeprecationWarning: Python 3.6 is no longer supported by the Python core team. Therefore, support for it is deprecated in cryptography. The next release of cryptography (40.0) will be the last to support Python 3.6.

We've been catching this since cryptography 37 and 3977fee with:

cli/nextstrain/cli/aws/cognito/__init__.py

Lines 7 to 15 in f05e2f9

	# Ignore noisy warning from cryptography 37.0.0 about deprecated support for Python 3.6.
	with warnings.catch_warnings():
	warnings.filterwarnings(
	"ignore",
	message = "Python 3\\.6 is no longer supported by the Python core team\\. Therefore, support for it is deprecated in cryptography and will be removed in a future release\\.",
	category = UserWarning)
	import jwt
	import jwt.exceptions

but cryptography 39 just released on 1 Jan changed the warning message so we now fail to silence it.

[tsibley]

Annoyingly, I noticed this when attempting to release 6.0.1 with changes I prepped for release 2 weeks ago (before I got the flu and before the holidays). So I'll need to fix it and release 6.0.1.post1 or something silly. This is a slightly annoying property of the order of operations of the release process. In some ways it'd be nicer to say, "ok, designate this successful CI build as release X.Y.Z" rather than "consider this source code X.Y.Z and run the CI release process; hopefully it doesn't fail!".