TYPO: fix typo in __all__ mass models

[ColmTalbot]

Fixes #111

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.43%. Comparing base (579db54) to head (af5c25a).
Report is 1 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
- Coverage   94.55%   94.43%   -0.12%     
==========================================
  Files          11       11              
  Lines         808      808              
==========================================
- Hits          764      763       -1     
- Misses         44       45       +1     

Flag	Coverage Δ
python3.10	94.43% <ø> (-0.12%)	⬇️
python3.11	94.43% <ø> (-0.12%)	⬇️

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