What is ‘GitHub Next’? Is this an official GitHub project? It’s not on the github.com domain, so it doesn’t look like it. What signals do I have to know that this site is trustworthy?

I click ‘get started’, and it wants me to hand over access to my GitHub account to see all private resources I have and "act on [my] behalf" to some unknown "blocks" third party.

How do I determine whether this website is some kind of phishing scam, or legit? Everything everyone always says ("check the domain!") rings alarm bells.