ci: Use micromamba 2.6.0

[jjerphan]

Description

Type of Change

• Bugfix
• Feature / enhancement
• CI / Documentation
• Maintenance

Checklist

• My code follows the general style and conventions of the codebase, ensuring consistency
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run pre-commit run --all locally in the source folder and confirmed that there are no linter errors.
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.28%. Comparing base (45a04df) to head (bdbfeee).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4280      +/-   ##
==========================================
+ Coverage   54.06%   54.28%   +0.22%     
==========================================
  Files         240      240              
  Lines       29876    29937      +61     
  Branches     3196     3204       +8     
==========================================
+ Hits        16153    16252      +99     
+ Misses      13720    13682      -38     
  Partials        3        3              

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[Klaim]

LGTM (on principle, once the CI passes)