Lift test fixes

[wd60622]

Description

Related Issue

• [x] Closes #644
• [ ] Related to #

Checklist

• [ ] Checked that the pre-commit linting/style checks pass
• [ ] Included tests that prove the fix is effective or that the new feature works
• [ ] Added necessary documentation (docstrings and/or example notebooks)
• [ ] If you are a pro: each commit corresponds to a relevant logical change

Modules affected

• [x] MMM
• [ ] CLV

Type of change

• [ ] New feature / enhancement
• [x] Bug fix
• [ ] Documentation
• [ ] Maintenance
• [ ] Other (please specify):

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📚 Documentation preview 📚: https://pymc-marketing--656.org.readthedocs.build/en/656/

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.74%. Comparing base (41dda4f) to head (bf9b34c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #656      +/-   ##
==========================================
+ Coverage   91.72%   91.74%   +0.02%     
==========================================
  Files          22       22              
  Lines        2321     2327       +6     
==========================================
+ Hits         2129     2135       +6     
  Misses        192      192              

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[juanitorduz]

Thanks @wd60622 !