SPM: specify a .git extension

[elfenlaid]

Danger: This can cause Xcode to not even want to start building: https://stackoverflow.com/q/63079909/3939277

adding .git to the end of the URL will solve that, and also might fix the thing down below where you had to use .product

Thanks for a nice catch :) Originally posted by @BenLeggiero in https://github.com/arthurpalves/badgy/pull/23