You publish your code in plaintext, it goes to github where someone reads it through some fancyfying code formatter that github applies to it and which might not even do the same ligatures as your editor. I'm not saying this is a dire problem, or a problem with you or even this specific font - rather the idea of ligatures in program source code to begin with, somewhat similar to using code identifiers (as opposed to literals or comments) outside of ascii-compatible characters of unicode.

That's not a very good thing, especially considering that there are (probably ?) actual unicode characters '→' and '≡' that are not valid syntax for -> and === in languages that utilize the later.