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

[yyccbb]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• 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: ☑️

• 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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.88%. Comparing base (9c33eb4) to head (94ad60b).
⚠️ Report is 179 commits behind head on master.

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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