Andromeda: fix numpy error due to dividing a boolean array

[IainHammond]

I was getting a critical error when running Andromeda with homogeneous_variance=False, looks like it was just a problem with modern numpy being strict

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 50.28%. Comparing base (38413c5) to head (6f333b0).
⚠️ Report is 11 commits behind head on master.

Files with missing lines	Patch %	Lines
src/vip_hci/invprob/andromeda.py	0.00%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #712      +/-   ##
==========================================
- Coverage   50.28%   50.28%   -0.01%     
==========================================
  Files          88       88              
  Lines       17058    17058              
==========================================
- Hits         8578     8577       -1     
- Misses       8480     8481       +1     

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[VChristiaens]

Thanks for the PR @IainHammond !