Add debian folder to gitignore

[ann0see]

Short description of changes
Until now a debian folder might have been commited to git.

I remember thinking of this some time ago where it didn't work as expected. However now I can verify that the debian/ folder is no longer added to git. I hope it doesn't have any side-effects I can't remember.

CHANGELOG: Internal: Add debian/ folder to .gitignore file to ensure build files are not added to git

Context: Fixes an issue?
Often while developing locally, I had to manually choose the files & changes I made. Now a git add . should be enough

Does this change need documentation? What needs to be documented and how?
No.

Status of this Pull Request
Works locally, should have another review

What is missing until this pull request can be merged?
Review

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above