make Xcode/CLT installation guard in Xcode.uncached_version more readable (replace unless with if and inversion)
make Xcode/CLT installation guard in Xcode.uncached_version more readable (replace unless with if and inversion)

woodruffw/homebrew-test,woodruffw/homebrew-test,woodruffw/homebrew-test,woodruffw/homebrew-test