fixes ci-cd issues

[tclose]

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Summary

• Fixes broken mrtrix conda install in docs build
• Install numpy < 2 in slurm build job

Checklist

• I have added tests to cover my changes (if necessary)
• I have updated documentation (if necessary)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.79%. Comparing base (47c3958) to head (281fc48).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
+ Coverage   87.89%   88.79%   +0.89%     
==========================================
  Files          84       84              
  Lines       17890    17890              
  Branches     3483     3483              
==========================================
+ Hits        15725    15885     +160     
+ Misses       1809     1635     -174     
- Partials      356      370      +14     

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