Watch out for the (presumably old) GitHub organization in .gitmodules: https://github.com/highlight/highlight/blob/d818969acddd7c74...
OT1H, GH does a 301 to the new name, but OTOH unknown how long that lasts and is one more thing to go off the rails for fresh clones. It has been my experience that using the https URL makes clones easier for users which may not have set up ssh auth, but it depends on the target audience and whether you have some internal tooling that depends on that submodule coming down over ssh