Hi:

I reached out to the developer, Max Horn, and the GitHub repository is an unofficial mirror and is manually updated by the developer on occasion. The only official source is https://pages.uoregon.edu/koch/texshop/ and the label should use that source.

So, I have the following updated TeXShop label:

texshop)
    name="TeXShop"
    type="zip"
    downloadURL="https://pages.uoregon.edu/koch/texshop/texshop-64/texshop.zip"
    expectedTeamID="RBGCY5RJWM"
    ;;