Do they gain the flight since the flight doesn’t require a feat? Apologies if this has been mentioned already.
Changing Shape just makes you look like another ancestry, it doesn't give you any of their abilities unless a later feat explicitly and specifically gives you something that that ancestry has. I know there are options for natural attacks and extra arms, I don't remember any feats granting flight options that something you're imitating has.
Some ancestries are not practical to imitiate because they come with inherent abilities that can't be imitated by an Astrazoan.