Only the copyright holder can decide the license of a work. When one uploads to GitHub, one grants GitHub some rights to use the code (e.g., to store and process it, to copy it, etc.) which would otherwise be infringed by copyright, but those rights don't include allowing others to exercise those rights without restriction. If that were the case, many users would not be willing to upload their code to GitHub, and in many cases, uploading content to GitHub would violate the terms of the license if there were outside contributors who hadn't agreed to those terms.
Typically, the license in a repository covers the entire project including CI scripts and other tools, but if you're unsure, you should ask. Asking politely about licensing in an appropriate forum to make sure you understand is generally fine and most projects will appreciate that you are trying to do your best to honor the terms of their license.
Note that the MIT License does require you to reproduce the copyright and license as a condition (that's the second paragraph). However, if your project is already MIT licensed, you can just add the copyright notice to your existing copyright notice, since you're already distributing the license.