Good point, it doesn’t appear to be. Might be good to drop a note on GitHub (or their contact method of choice) so they can set that flag.
Edit: I just went and sent them a mention on Mastodon. I noticed it’s an admin account so I wonder if Lemmy lets both flags be set at once.
My understanding is that you’re not going to find a self hosted solution that makes use of SMS (not counting email to SMS gateways) because sending SMS programmatically requires a SMS gateway those aren’t cheap (think of Twilio). You can find many options for app-based notifications (push notifications usually) and email-based notifications as a workaround.