fix LaTeX dot in diversification ratio formula

[saishreyakumar]

Description

Replaced \cdot with . in the LaTeX formula for the diversification ratio in the docstring to fix the rendering issue.

Related Issue

• Closes Poor rendering of latex documentation #1777
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass. Feel free to comment pre-commit.ci autofix to auto-fix.
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks) using numpydoc format.
• If you are a pro: each commit corresponds to a relevant logical change

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📚 Documentation preview 📚: https://pymc-marketing--1788.org.readthedocs.build/en/1788/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.84%. Comparing base (a97c4db) to head (730fc65).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1788   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files          60       60           
  Lines        6819     6819           
=======================================
  Hits         6263     6263           
  Misses        556      556           

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[williambdean]

Thanks for the edits @saishreyakumar

I'm see some issues with it still
https://pymc-marketing--1788.org.readthedocs.build/en/1788/api/generated/pymc_marketing.mmm.utility.diversification_ratio.html#pymc_marketing.mmm.utility.diversification_ratio