It will try to connect to the correct port, but fetch the wrong SSH host key as it tried to fetch on port 22 (Which is caused the way ssh-keyscan handles ports as you have to pass the port by -p )
As a workaround:
Manually fetch the correct key and then put it into the known_hosts file generated by this plugin.
I recently encountered a little bug in the git plugin of yours.
When you specify the following service block in the caddy file:
git { repo ssh://git@git.example.ch:7999/git/repo.git key /etc/caddy/id_rsa path /var/www/repo }
It will try to connect to the correct port, but fetch the wrong SSH host key as it tried to fetch on port 22 (Which is caused the way ssh-keyscan handles ports as you have to pass the port by -p)
As a workaround: Manually fetch the correct key and then put it into the known_hosts file generated by this plugin.