There is demographic information, but you aren't using it. Fundamentally the equation holds:

    hiring_procedureX(Candidate(github, male)) == hiring_procedureX(candidate(github, female))

There is nothing whatsoever preventing a person of any sort from creating a code portfolio, and it's pretty easy to browse a github profile without learning anything about the demographics of the coder.

In contrast, basically every other screening procedure out there is potentially influenced by the demographics of an applicant. Prior employers/educators might have been racist/sexist, interviews are potentially subject to similar biases, etc.