Same problem here. Until there's a fix, the workaround is
- Download and unzip the .img.gz
- Erase the SD card via Disk Utility as MS FAT (MBR)
- Confirm which disk it is, in my case, /dev/disk2
- Unmount via diskutil so you don't get a Resource Busy error (doing it via UI did not work for me as CLI would not see the SD anymore)
- Copy the image to SD using dd
That should do it.