Update to f24: Error: Package xxxxx.rpm is not signed

sudo dnf system-upgrade download --releasever=24 --allowerasing -y

...  freetype                       i686   2.6.3-2.fc24               fedora  366 k  freetype                       x86_64 2.6.3-2.fc24               fedora  360 k  freetype-devel                 x86_64 2.6.3-2.fc24               fedora  447 k  freetype-freeworld             x86_64 2.5.5-2.fc24               rpmfusion-free-updates-testing ... The downloaded packages were saved in cache until the next successful transaction. You can remove cached packages by executing 'dnf clean packages'. Error: Package freetype-freeworld-2.5.5-2.fc24.x86_64.rpm is not signed