Indentation is corrupted when I post a file to GitHub, when it looks OK in Notepad++ and VS Code

I have some weird issue: It's not very important, but I want my code to look nice on GitHub.

I've implemented MergeSort in AEC, and I posted it to GitHub, you can see it here.
However, the indentation doesn't look the same as it does in Notepad++ or VS Code, here is how the lines 101-107 look if I open that file in Notepad++:

I don't expect syntax highlighting to work on GitHub, the syntax highlighting for AEC works in Notepad++ because I opened the Notepad++ script to highlight AEC code.
However, I would expect the indentation to look the same whether it's on GitHub or in a text editor.
So, why it doesn't?