We started migrating some of our projects lately from Cocoapods to SwiftPM, and faced exactly the same issue. Took many hours since the stacktrace was not giving enough information, and using reductio ad absurdum I managed to locate a problematic Swift Package (in my case it was the UIColor-Hex-Swift package). Weirdly enough, this issue is occurring only when used as Swift Package and not as a Cocoapods Dependency.

This is issue is very old (I initially faced it on Xcode 11) and I wonder why Apple has not fixed it yet. There are many times that you are working for multiple companies or for customers of your company that have their own workspaces set up and provide different email addresses to software engineers. Every time I need to add a Swift Package dependency I have to rename my ~/.gitconfig and then remember to name it back with the proper name in order for this to work.