Remove mentions of Jekyll 4 & Pygments deprecation from about-github-pages-and-jekyll

[janbrasna]

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Fixes #30152

about-github-pages-and-jekyll.md#syntax-highlighting

Why:

The reason for deprecation is not correct. The package itself is not deprecated. Mention of Jekyll 4 is extremely confusing as GitHub Pages build using Jekyll 3.9.x …

For reference to commit logs adding the info cross referenced to package release versions see issue: Closes: #30152

What's being changed (if available, include any code snippets, screenshots, or gifs):

1. Removing unnecessary info not relevant to the highlighters' use.
2. Updating highlighter's repo link.
3. Adding alt highlighter's repo link.

Check off the following:

• [x] I have reviewed my changes in staging, available via the View deployment link in this PR's timeline (this link will be available after opening the PR).

  • For content changes, you will also see an automatically generated comment with links directly to pages you've modified. The comment won't appear if your PR only edits files in the data directory.

• [x] For content changes, I have completed the self-review checklist.

[github-actions[bot]]

Automatically generated comment ℹ️

This comment is automatically generated and will be overwritten every time changes are committed to this branch.

The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

You may find it useful to copy this table into the pull request summary. There you can edit it to share links to important articles or changes and to give a high-level overview of how the changes in your pull request support the overall goals of the pull request.

Source	Preview	Production	What Changed
pages/setting-up-a-github-pages-site-with-jekyll/about-github-pages-and-jekyll.md	fpt ghec ghes@ 3.12 3.11 3.10 3.9 3.8	fpt ghec ghes@ 3.12 3.11 3.10 3.9 3.8

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fpt: Free, Pro, Team ghec: GitHub Enterprise Cloud ghes: GitHub Enterprise Server

[nguyenalex836]

@janbrasna Thanks so much for opening a PR! I'll get this triaged for review ✨

[github-actions[bot]]

Thanks for opening a pull request! We've triaged this issue for technical review by a subject matter expert :eyes:

[nguyenalex836]

@janbrasna Thank you for your patience while our team reviewed! This looks great ✨ I'll update the branch and get this merged once tests are passing 🍏

[github-actions[bot]]

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