For users, the issue is already solved: Just do sudo dnf clean all and then sudo dnf update, or directly sudo dnf update --refresh. After that, you can work as usual with sudo dnf update or whatever interface you use for updates. The error should be gone now. The unsigned packages are no longer in the updates, which is not a problem because they are not security/compatibility critical at the moment. They will be added again when the issue in general is solved. But the users do not need to care about that.