Just create another account and shift your repo there. If it is your employment you are concerned about, you gotta bend the knee here coz one way or the other, someone will taste bad blood in the end. Who the fuck asks for GitHub password? Who the fuck asks for any password?
And if they are such geniuses, they should have blacklisted Github.com in their firewall when they had the chance and used and enterprise self-hosted Github server of their own to keep the company code. Boi, you are working with idiots I am telling you.