GitHub authorization for older account fabpot it set up using OAuth, while for new one FabienPotencier with GitHub Apps. More details on GitHub Apps are here, including this:
With GitHub App repository webhooks and deploy (SSH) keys stay untouched. Instead of adding a deploy (SSH) key to the repo the App uses an “installation” token for cloning the repo via HTTPS. That installation token is rotated hourly. To start new builds on push and pull requests, AppVeyor App uses a centralized webhook handler which is called by all app-enabled repos.