SSH authentication by Ghost user


I got a SSH private key from our Jenkins configuration. I don’t know whom it belogs to. So, I authenticated via SSH with this key and the welcome message shows:

login as: git
Authenticating with public key "imported-openssh-key"
Server refused to allocate pty
Welcome to GitLab, @ghost!

I cannot find the key’s fingerprint in any GitLab user’s SSH keys and the Ghost User doesn’t show any SSH keys.

How can I figure out whose key it is and how can I block it? Thanks!

Best regards!