And then you create an action on a schedule [0] which checks upstream for updates, and syncs it to your fork. Mind you that that sync needs to be done with a PAT [1], otherwise that sync (push) will not trigger a new build.

[0] https://docs.github.com/en/actions/writing-workflows/choosin...

[1] https://docs.github.com/en/actions/security-for-github-actio...

> When you use the repository's GITHUB_TOKEN to perform tasks, events triggered by the GITHUB_TOKEN, with the exception of workflow_dispatch and repository_dispatch, will not create a new workflow run. This prevents you from accidentally creating recursive workflow runs. For example, if a workflow run pushes code using the repository's GITHUB_TOKEN, a new workflow will not run even when the repository contains a workflow configured to run when push events occur.