wpt-829c50288: Build WPT package weekly (#8)

This is the really easy part of our idea to update WPT automatically. 

Unfortunately, we'll need to go into this repo and either make a useless commit or re-enable the workflow every 60 days. Thanks, Github

> In a public repository, scheduled workflows are automatically disabled when no repository activity has occurred in 60 days. For information on re-enabling a disabled workflow, see Disabling and enabling a workflow.