GH Apps already use short-lived tokens that can be scoped per repo. You mint a token using your private key and exchange it for a token via API. Then you use that token and dispose of it. That's the only way to use GH Apps (User Access Tokens which are the same thing, but require user interaction) Those tokens always expire.

I'd rather GitHub finally fix their registry to allow these GH Apps to push/pull with that instead of PAT.