I'm trying to import highlight css from my main site.scss file like:

@import "highlight-9.12.0/default"; -- there is a /_sass/highlight-9.12.0/default.css file

but jekyll serve fails with:

Conversion error: Jekyll::Converters::Scss encountered an error while converting 'assets/css/site.scss':
                    File to import not found or unreadable: highlight-9.12.0/default. Load path: /Users/marceloverdijk/my-site/_sass on line 20

I noticed #4527 but don't understand if it is solved or not.
Should importing without extension be supported?

I'm using Jekyll 3.7.3 and Sass 3.5.6 (deploying on GitHub pages).