bump to setup-micromamba v2 and checkout v4

[atravitz]

we were using v1 for a few workflows and v2 for others, so im moving us to use v2 everywhere.

edit: also bumping checkout to v4 for the same reason here.

Checklist

• Added a news entry

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.65%. Comparing base (e4adb62) to head (9615ed5).
⚠️ Report is 142 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1347      +/-   ##
==========================================
- Coverage   93.35%   92.65%   -0.71%     
==========================================
  Files         165      143      -22     
  Lines       12419    10994    -1425     
==========================================
- Hits        11594    10186    -1408     
+ Misses        825      808      -17     

Flag	Coverage Δ
fast-tests	92.65% <ø> (-0.71%)	⬇️

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[github-actions]

No API break detected ✅