Little Snitch is denying connections for GitHub Desktop via SSH. GitHub Desktop itself doesn't have a code signature issue according to Little Snitch. It's just the SSH executable it uses that does. I installed OpenSSH via Homebrew. Reinstalling it didn't seem to help.
How can I tell if I actually have an issue with SSH vs. just Little Snitch being incorrect (from a user perspective) in its blocking? I've disabled the rule, but if possible I'd like to resolve the root issue.