I don't have SSH access to GitHub configured on my machine, and
instead use/prefer the PAT (Personal Access Token) based access. In
any case, the submodule is a public repository, so the credentials
shouldn't matter. However, if we use the git:// URL for the submodule,
then git fails to fetch it if SSH isn't configured even if it is
public.
So use the less restrictive HTTPS based URL. This will work for
everyone, even if they haven't configured any private GitHub
credentials.
