Can I setup Gloud Cloud Build with a source repository shared to my github account?

Question

I am setting up a GCloud function on Cloud Run for a client. He has shared his repo with me on github so I can access it. However, when choose the 'continuously deploy from a repository' option and proceed to set up cloud build using my github credentials, the dropdown for repositories only shows the ones I created/own in my github account. The shared ones do not show up in this dropdown. Since I am supposed to be doing all the technical work for him, I do not want to have to ask for his credentials or do a pair programming session with him driving, unless I really have to. I also don't want the repo under my account since he should own the code.

So give all that, is there any way in Cloud Build setup, to connect to a source repository that is shared with me?