update python minimum to 3.8 and update cprnc module.

[jedwards4b]

Update min python version to 3.8
Also updates to latest cprnc version

Test suite:
Test baseline:
Test namelist changes:
Test status: [bit for bit, roundoff, climate changing]

Fixes #4032

User interface changes?:

Update gh-pages html (Y/N)?:

[rljacob]

Did you mean to update the cprnc submodule too?

[rljacob]

Can you also update the error message as below?

   msg = (
        "Python "
        + str(major)
        + ", minor version "
        + str(minor)
        + " is required to run CIME. You have "
        + str(sys.version_info[0])
        + "."
        + str(sys.version_info[1])

[jedwards4b]

Yes, I did intentionally update cprnc to the latest as well.

[rljacob]

Since we test as far back as 3.8, does that mean those tests will fail as soon as we use some python thing that is NOT in 3.8? That would then tell us to either update this string again or try a different 3.8-friendly approach.

[jedwards4b]

That's almost correct - unfortunately this test is not comprehensive and the code that @jgfouca mentioned in system_tests_common.py is not exercised here.

[jgfouca]

We should probably just refactor that code instead of bumping up the min python. It's just one call to datetime.fromisoformat. The thing that I don't understand is that we see fails from py3.9 but the online documentation says support for fromisoformat was added in py.3.7. The error does go away if we use 3.11

[jedwards4b]

Updated datetime to be backward compatible.