Syntax highlighting for Agda does not work
### Summary
GitLab does not seem to do syntax highlighting for [Agda](https://en.wikipedia.org/wiki/Agda_(programming_language)) programs despite correctly recognising them to be written in Agda.
### Steps to reproduce
Trivial. See the following section.
### Example Project
https://gitlab.com/ayberkt/agda-highlighting-issue/blob/master/Foo.agda
### What is the current *bug* behavior?
Agda programs are displayed without syntax highlighting. I am not entirely sure this is *bug* behaviour but I would expect GitLab to do syntax highlighting for every program whose language it can recognise. Therefore I decided to classify this as a bug rather than a feature request.
### Output of checks
This bug happens on GitLab.com.
issue