ssh clone not working with github

As per GitHub help, the error you're getting is related to wrong SSH configuration. Please follow indications for setting up SSH for GitHub and check accordingly.

You can either follow the below document to add your key to ssh-agent https://help.github.com/en/articles/connecting-to-github-with-ssh

or you can run the following command to execute it temporarily

ssh-agent bash -c 'ssh-add ~/.ssh/github_rsa; git clone git://github.com/npsabari/testrepo.git'