Fix gap between lines in source viewer (Chrome)

What does this MR do and why?

Fixes a minor bug in Chrome where a small gap was rendered between line numbers when viewing source files.

⚠ changes are behind the highlight_js feature flag

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Enable the highlight_js feature flag
2. View a source file

MR acceptance checklist

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