私もそれ (関連しうる他のリポジトリも含めて) で出なかったのと，https://cs.github.com/?scopeName=All+repos&scope=&q=SPMRepositoryError の結果から，Xcode.app の IDESwiftPackageCore.framework が持っている型だろうなと判断しました． (edited)
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$ nm -g /Applications/Xcode-13.3.0.app/Contents/PlugIns/IDESwiftPackageCore.framework/Versions/A/Frameworks/SwiftPM.framework/SwiftPM | grep SPMRepositoryError 000000000006f64c T _$s7SwiftPM18SPMRepositoryErrorO010underlyingD010repositoryACSgSo7NSErrorC_So32DVTSourceControlRemoteRepositoryCSgtcfC 00000000005ae108 S _$s7SwiftPM18SPMRepositoryErrorO10Foundation09LocalizedD0AAMc 00000000005ae178 S _$s7SwiftPM18SPMRepositoryErrorO10TSCUtility27DiagnosticLocationProvidingAAMc 00000000006b0ba8 S _$s7SwiftPM18SPMRepositoryErrorO10TSCUtility27DiagnosticLocationProvidingAAWP 000000000006f9e8 T _$s7SwiftPM18SPMRepositoryErrorO11descriptionSSvg 00000000005ae1d8 S _$s7SwiftPM18SPMRepositoryErrorO11descriptionSSvpMV 000000000006f684 T _$s7SwiftPM18SPMRepositoryErrorO16errorDescriptionSSvg 00000000005ae1d8 S _$s7SwiftPM18SPMRepositoryErrorO16errorDescriptionSSvpMV 000000000006f9ec T _$s7SwiftPM18SPMRepositoryErrorO18diagnosticLocation8TSCBasic010DiagnosticF0_pSgvg 00000000005ae1d8 S _$s7SwiftPM18SPMRepositoryErrorO18diagnosticLocation8TSCBasic010DiagnosticF0_pSgvpMV 0000000000073e54 T _$s7SwiftPM18SPMRepositoryErrorOMa 00000000005ae204 S _$s7SwiftPM18SPMRepositoryErrorOMn 00000000006b0c78 S _$s7SwiftPM18SPMRepositoryErrorON 00000000005ae188 S _$s7SwiftPM18SPMRepositoryErrorOs0D0AAMc 00000000005ae150 S _$s7SwiftPM18SPMRepositoryErrorOs23CustomStringConvertibleAAMc