As the parent comment describes: You're using Gitlab as a web interface to change code on your servers. Javascript running on the page of that web interface can do almost anything you can do with that page, by producing the same events.
(actually, browsers have a bunch of tools to restrict that, so it's not 100 % if engineered properly. But if it's just "include some scripts"...)
In what universe would javascript running on a webpage be able to access (nevermind modify) the filesystem on the server.