Not to mention Twitter is not an open platform anymore! (A) I'm an employee in an organization paying for Github. (B) I don't have a Twitter account. I already have a Github account because of (A). Why should (B) stop/delay me from getting official comms about this?
It's not "spam" if it is relevant to me, such as security incident disclosures.
Also, as tiffanyh pointed out, what's wrong with Github blog or is that exclusively for marketing fluff now? That would've been appropriate enough, without having to spend Sendgrid credits.