+1 to the DTS Engineer's recommendation to file a bug report. Also: Have you tried creating a new Xcode Cloud workflow which just performs a Build action without attempting to run any tests? I'd be curious if that would succeed and how long it would take.

Are you attempting to run builds directly against the repository at https://github.com/google/googlesignin-ios, a branch on that repo, or have you created your own fork of their repo? Also, are you able to attach the .xcresult file?