Tests: use `tar` rather than `echo` for sandbox test on Windows (#5513)
Tests: use `tar` rather than `echo` for sandbox test on Windows (#5513)

`echo` is a `cmd` shell builtin and not available as a standalone binary
as from coretuils on Linux.  It should be noted that `echo` is available
as a shell builtin on Linux and is not required to be provided as a core
binary.  `tar` is only available on more recent Windows releases with 10
or newer.
abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager