Eeh, you always rely on someone else's infrastructure. Even if you are off cloud entirely and own your own datacenter, you still need peering/transit. You still need power (or at least fuel). You can't avoid depending on a DNS infrastructure.

Github does have an SLA: https://github.com/customer-terms/github-online-services-sla. But like virtually all SLAs, it's really just a token gesture. I have never seen an SLA that pays the losses you suffer due to the outage.