Not sure how you see git repos as a compute intensive process. A single git commit takes milliseconds. It's mostly a hash calculation and a small file transaction. They've added some database stuff around the edges, but that is pretty tame as well.

Actions are unbounded, take minutes to resolve - sometimes hours and there are megabytes, gigabytes of network transactions.

Scaling commits is a load balancer and some more instances of a thing you’ve built over and over.

Scaling actions is VMs, networking, imbalances in load, memory, insuring that folks aren’t running VM training against your infrastructure. Oh, and maybe you want to make sure folks aren’t trying to hack that infrastructure as well.

It is a very, very hard problem.