pin macos runners to macos-12

[mikemhenry]

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[mikemhenry]

I think we should make macos-latest not a required check until we get the missing deps onto conda-forge, but we should keep it in the build matrix.

We should make macos-13 a required check.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.32%. Comparing base (378147c) to head (059ceda).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #841      +/-   ##
==========================================
- Coverage   94.13%   92.32%   -1.81%     
==========================================
  Files         134      134              
  Lines        9786     9786              
==========================================
- Hits         9212     9035     -177     
- Misses        574      751     +177     

Flag	Coverage Δ
fast-tests	92.32% <ø> (?)
slow-tests	?

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[mikemhenry]

We got one missing dep, a weird package hash error, and a issue with ambertools/charge backend :)

[IAlibay]

@mikemhenry for the sake of "getting CI back and running today", let's go with just pinning to macos-13. I've opened a separate issue to deal with arm64-osx in a separate PR.

[IAlibay]

self-approving