It would still be a CFAA violation for the employer to use those keys to act as the employee against a third-party serivce like Github. So the employee might no

It would still be a CFAA violation for the employer to use those keys to act as the employee against a third-party serivce like Github. So the employee might not be able to object to them seeing that, but they would have no right to use them to access the employee's account on a remote server. Just like if they found a check on your desk they can look at the numbers, but they can't just use them to take money out. Also, you could and probably should create a new SSH key on the company laptop or a personal access token for HTTPS access so that it can be easily revoked when you leave.