Update dependency mathjax to v2.7.9 - autoclosed

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
mathjax (source)	patch	2.7.7 -> 2.7.9

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Release Notes

mathjax/MathJax (mathjax)

### [`v2.7.9`](https://redirect.github.com/mathjax/MathJax/releases/tag/2.7.9): MathJax v2.7.9 [Compare Source](https://redirect.github.com/mathjax/MathJax/compare/2.7.7...2.7.9) This release updates the Speech-Rule Engine (SRE) that underlies MathJax's accessibility features to version 3.1 and updates the a11y extensions to version 1.6.0 to take advantage of the new SRE version. The upgrade includes new languages (German and French), and access to the Clearspeak rules via the accessibility menu, as well as bug fixes in SRE, and faster conversion of expressions to speech.

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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