[WorkspaceTests] Add in memory git functionality in MockManifestGraph
[WorkspaceTests] Add in memory git functionality in MockManifestGraph

abertelrud/swift-package-manager,abertelrud/swift-package-manager,vmanot/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,vmanot/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,JGiola/swift-package-manager,JGiola/swift-package-manager,abertelrud/swift-package-manager