The 2nd gen Cloud Build repositories configuration prompts for OAuth authentication as an individual. We don't really want to do that.
We replicated the 1st gen configuration from the prior repository location, which involved attaching the Cloud Build GitHub App to this repository. (A nice thing: this doesn't involve any individual's credentials.)
We talked about running CI from GH Actions, and using workload identity for authentication, so all the "deployment" authentication and authorization is on the GAE.
But... it looks like it works, we got deploys running!
Per @stillgreenmoss : we need to fix the Cloud Build config, as it's pointing to stillgreenmoss/pairing-bot instead of recursecenter/pairing-bot.