Comment by nicolas-p

I have just tried it on my older Mac that still runs El Capitan. I downloaded the image from the website, opened it and copied the folder to the desktop. I had the same error as you ("Skov is damaged and can't be opened"). Then I went to System Preferences > Security and Confidentiality and I saw that "Allow applications downloaded from" was set to "Mac App Store and identified developers". I selected "Anywhere" and tried again: it worked. So the problem was really Gatekeeper.