IANAL, but this appears to be a breach of the Equality Act 2010. Are they offering this in the UK?
If you'd like to get your local Scouts group to work on code within the safe measures of private repos, I'm sure you'd also find sponsors. It's not a breach of Equality when you aren't stopping other people from doing something. I'm sure Github would love sponsorship from all over the place. A benefit of this is clever on Ada and Github's part: a lot of women don't participate in code sharing because of reasons that…
The commentary I've seen on the Equality Act states that, for example, situations where nightclubs offer free entry to women might fall foul of the Act.
This seems comparable.