Putting this into the global section of ssh_config is evil. The foreman-proxy remote execution picks the correct identity file on the command line. Don’t refer to it in ssh_config. All other users except root and foreman-proxy may not be able to use ssh anymore because they cannot read the identify file…
I think the easiest way to find out what is happening is to run this exact command as foreman-proxy user.
If you rely on setting a ProxyCommand then it won’t work. foreman-proxy user intentionally has no shell configured to prevent logins. It cannot execute the ProxyCommand. That’s why the ssh call explicitly sets ProxyCommand=none. See All remote execution jobs fail immediately with exception