repos: Don't panic if we find unknown external service kind
Created by: ryanslade
The function already returns an error so it should be fine to return an error instead of panicking
Fixes: https://github.com/sourcegraph/sourcegraph/issues/22894
Created by: ryanslade
The function already returns an error so it should be fine to return an error instead of panicking
Fixes: https://github.com/sourcegraph/sourcegraph/issues/22894