[ Oops, I hit 'send' before I meant to. ]
As I was saying, I'm seeing this same behavior. Downgrading to libssh-0.7.5-7.fc28[1]
and version locking the package[2] eliminates the error/warning.
[1] dnf install libssh-0.7.5-7.fc28
[2] dnf versionlock add libssh-0.7.5-7.fc28