Bump highligh.js and lowlight syntax highlighting

What does this MR do and why?

This MR bumps highlight.js to 11.15.1 and lowlight to 2.6.1 to add some improvements to syntax highlighting on GitLab.

• Full highlight.js changelog
• Full lowlight changelog

Screenshots or screen recordings

There are no visual differences noted between the two versions.

Before	After

How to set up and validate locally

1. In rails console enable the hightlight_js experiment fully

   Feature.enable(:hightlight_js)

2. View a file http://gdk.test:3000/gitlab-org/gitlab-shell/-/blob/main/client/httpclient.go
3. Confirm the syntax highlight is not visually different compared to the file in production

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.