Confusing error when an OpenSAFELY upgrade is available, but unsupported by installed Python

I'll put this here for discussion in case it's worth bothering to handle nicely.

Issue reproduction

From this support question:

Every time I submit command in my Anaconda prompt I'm told that v1.17.1 of opensafely is available (I currently have 1.15.1). But everytime I run , it says it cannot find a version that satisfies the requirement for opensafely =1.17.1 (despite listing 1.15.1 in the list of options).

I believe the cause is:

• Have opensafely correctly installed on Python 3.7
• Run opensafely which tells you to run opensafely upgrade
• Run opensafely upgrade which fails because there is no package suitable for Python 3.8

It's a confusing error for a non-developer, because it makes it seem like the CLI is trying to pull a non-existent version:

ERROR: Could not find a version that satisfies the requirement opensafely==1.20.0 (from versions: 1.0.1, 1.0.2, 1.1.0, 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.2.0, 1.2.1, 1.3.0, 1.3.1, 1.3.2, 1.3.3, 1.3.4, 1.4.0, 1.4.1, 1.4.2, 1.5.0, 1.5.1, 1.6.0, 1.6.1, 1.6.2, 1.6.3, 1.6.4, 1.7.0, 1.7.1, 1.7.2, 1.8.0, 1.8.1, 1.9.0, 1.9.1, 1.9.2, 1.10.0, 1.10.1, 1.10.2, 1.10.3, 1.11.0, 1.11.1, 1.11.2, 1.12.0, 1.13.0, 1.14.0, 1.15.0, 1.15.1)
ERROR: No matching distribution found for opensafely==1.20.0

Possible fix

We just need to check when upgrading, maybe something[^1] like:

import platform
from packaging.specifiers import SpecifierSet

# resp here is https://pypi.org/pypi/opensafely/json as a dict
version_specifier = SpecifierSet(resp["info"]["requires_python"])

if (python_version :=  platform.python_version()) not in version_specifier:
    raise Exception(f"The latest OpenSAFELY CLI does not support {python_version}; please upgrade your Python.")

[^1]: I think this would be the canonical Python way of checking, but feel free to correct me.

Start in opensafely/upgrade.py around lines 72-75 and inspect how the PyPI response and installed Python version are handled during an upgrade. Reproduce the upgrade on an unsupported Python version, then verify that the CLI reports the compatibility problem clearly instead of exposing pip's confusing version error.