There are plenty of places where I, as a competent white male, can get hired and promoted without difficulty. The fact that Github isn't one of those is not a systematic problem. More power to them.
Github is a major software company, and there are similar signs at other major companies, most of whom are starting down a similar path.
When it's actually hard to get a job as a white male developer. We're very far from that point.
I think it's reasonable to worry well before that.
(I don't know what if anything we can or should do aside from worry.)
I don't know what your definition of major is, but Github is not it in my book. Don't get me wrong, they make a semi-decent product, better than anyone else at this point, but they are by no means the only solution in their market.
Hey, very scary to hear you say that. My email is in my profile. Write me anytime if you want. Lots of people on HN love to help other people. Don't be shy about reaching out.
That said, I don't think I "prefer" anything about the way the world works now.