No. But it eases "man in the middle" attacks (someone impersonating the host you think you're connecting to, with that key).
Still, if someone puts your pub key in an authorized_keys of a malicious host, and then manipulates your DNS or ARP to conduct you to such host, you should get some SSH warnings about the host fingerprint, etc.
And still, if you're using a dedicated key, the only possible attack could be to make you commit your repo changes, to the malicious machine instead of to github.
Still, if someone puts your pub key in an authorized_keys of a malicious host, and then manipulates your DNS or ARP to conduct you to such host, you should get some SSH warnings about the host fingerprint, etc.
And still, if you're using a dedicated key, the only possible attack could be to make you commit your repo changes, to the malicious machine instead of to github.