Hi,
your client doesn’t offer an SSH key, the automated lookup fails. You might want to configure a different path in your local .ssh/config file, or for testing, pass it via the -i parameter.
Also, please note that you will be logged out immediately after a successful SSH login attempt as the git shell is not a real unix shell.
See my test:
ssh git@gitlab.com
The authenticity of host 'gitlab.com (2606:4700:90:0:f22e:fbec:5bed:a9b9)' can't be established.
ECDSA key fingerprint is SHA256:HbW3g8zUjNSksFbqTiUWPWg2Bq1x8xdGUrliXFzSnUw.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'gitlab.com,2606:4700:90:0:f22e:fbec:5bed:a9b9' (ECDSA) to the list of known hosts.
PTY allocation request failed on channel 0
Welcome to GitLab, @dnsmichi!
Connection to gitlab.com closed.
Cheers,
Michael