Clone a private repo on a computer with multiple GitHub accounts
Solution 1:
If the specified keypair is not being honored, try enabling the IdentitiesOnly option. The client might be using the wrong key from ssh-agent.
Test using ssh githubpersonal – make sure the server greets you with the expected GitHub account name.
The user.* settings are not used for authentication. The Git protocol has no authentication of its own, only the one provided by SSH (or HTTPS).