Change submodule URL to use HTTPS

[VeryUsual]

Change submodule URL to use HTTPS to ensure easier access for all contributors in areas where SSH keys may not be available

[jzohrab]

Thank you @VeryUsual . I've never bothered to look into the difference between these, but it does look like https is better for a casual, open team. Anki uses https as well in their repo (ref https://github.com/ankitects/anki/blob/main/.gitmodules). Devs can override that to ssh if they want -- git config submodule.<name>.url git@github.com:org/repo.git

I don't see why the tests failed, I'll rerun the job.

I'll also try out another local clone to see what cred prompts or anything I get, b/c that would need to be documented for new devs.

[jzohrab]

Hm repeated failures, though the submodule checkout succeeded in CI. Not sure why, will try running the dev line in CI again.

[jzohrab]

Continues to die after repeat reruns. I'll have to try this locally to see if I can sort out what's up, as this doesn't make sense that it would fail after a successful checkout.