Fix hljs comments bug

What does this MR do and why?

Fixes a bug where comments was not correctly displayed when highlighting with highlight.js.

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Enable the highlight_js feature flag
2. View a file containing a mixture of code, multi-line and single-line comments
3. The file should highlight correctly

MR acceptance checklist

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