Bump to py3.9, test py3.12

[codecov[bot]]

Codecov Report

Merging #475 (9c47f1f) into main (e3254bd) will decrease coverage by 0.21%. The diff coverage is 91.17%.

:exclamation: Current head 9c47f1f differs from pull request most recent head 6aa8bd1. Consider uploading reports for the commit 6aa8bd1 to get more accurate results

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
- Coverage   86.30%   86.10%   -0.21%     
==========================================
  Files          22       22              
  Lines        4185     4209      +24     
  Branches      211      207       -4     
==========================================
+ Hits         3612     3624      +12     
- Misses        515      528      +13     
+ Partials       58       57       -1     

Flag	Coverage Δ
mypy	38.00% <56.25%> (+0.92%)	:arrow_up:
unittests	95.85% <100.00%> (-0.13%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cf_xarray/accessor.py	85.99% <100.00%> (-0.47%)	:arrow_down:
cf_xarray/criteria.py	99.06% <100.00%> (+<0.01%)	:arrow_up:
cf_xarray/formatting.py	76.66% <100.00%> (-0.26%)	:arrow_down:
cf_xarray/geometry.py	88.33% <100.00%> (ø)
cf_xarray/helpers.py	65.81% <100.00%> (ø)
cf_xarray/options.py	92.59% <100.00%> (+0.28%)	:arrow_up:
cf_xarray/scripts/make_doc.py	96.42% <100.00%> (ø)
cf_xarray/utils.py	89.18% <100.00%> (+0.14%)	:arrow_up:
cf_xarray/tests/test_accessor.py	94.06% <80.00%> (-0.06%)	:arrow_down:

... and 2 files with indirect coverage changes

[dcherian]

~myst-nb only supports py3.10. I think this is why I was getting weird behaviour?~

Don't know but by moving myst-nb to doc.yml, we now get a consistent environment at least.