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?
SPConradWTree
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+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.