Fix markdown-it-texmath rendering of /[a-z]+\*/ format environments

[yyccbb]

What is the purpose of this pull request?

• [ ] Documentation update
• [x] Bug fix
• [x] Feature addition or enhancement
• [ ] Code maintenance
• [ ] DevOps
• [ ] Improve developer experience
• [ ] Others, please explain:

Closes #2709 Overview of changes:

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)

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Checklist: :ballot_box_with_check:

• [ ] Updated the documentation for feature additions and enhancements
• [ ] Added tests for bug fixes or features
• [ ] Linked all related issues
• [ ] No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• [ ] Major (when you make incompatible API changes)
• [ ] Minor (when you add functionality in a backward compatible manner)
• [ ] Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov[bot]]

Codecov Report

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

Project coverage is 52.88%. Comparing base (9c33eb4) to head (94ad60b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2711      +/-   ##
==========================================
+ Coverage   52.84%   52.88%   +0.03%     
==========================================
  Files         130      131       +1     
  Lines        7162     7167       +5     
  Branches     1503     1501       -2     
==========================================
+ Hits         3785     3790       +5     
- Misses       3072     3222     +150     
+ Partials      305      155     -150     

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