refactor: use new versions of environment variables

[romanc]

Description

The old ones are currently deprecated and expected to be removed in the future (after a grace period). See NOAA-GFDL/NDSL#193 for more details.

How Has This Been Tested?

All good as long as CI is still green.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas: N/A
• I have made corresponding changes to the documentation: N/A
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included: N/A
• Targeted model if this changed was triggered by a model need/shortcoming: N/A

[romanc]

This should be good to merge now that NOAA-GFDL/pySHiELD#60 has landed. Can someone with access rights push the button? Thanks! 🙏

[romanc]

@fmalatino I noticed you also tried to re-run the pyshield test. Re-running (and I always forget this) will re-run the test as it ran last time, meaning it will go and fetch the old version of pyshield (the one that doesn't have the patch yet). Are the failing pyshield tests blocking you from putting that PR into the merge queue? If so, I can force update the PR to trigger a new run of the pyshield tests (which will include your fixes and should thus pass). If not, I suggest you just put it into the merge queue because the merge queue will trigger tests again (with the new version of pyshield this time).

[romanc]

Looks like auto-merge was waiting for an initial round of green tests. I've pushed a small change to the README file removing the ```shell line from this code block

That will run new tests and - if I understand auto-merge correctly - will just go ahead and put the PR automatically in the merge queue once the initial round of tests comes back green.