It's probably a matter of taste - but I think they should be in the same repo. I like tying test failures/regressions to a specific commit for documentation and admin purposes. Having a test fail or regression due to an 'unrelated' commit in another repo sounds like a nightmare waiting to happen when you try investigating.

I the difference of opinion is between developers who work on self-hosted "evergreen" products where the latest version is deployed, and others who work with multiple release branches with fixes/features constantly being cherry-picked.