You’re not gonna be able to do it entirely within github actions. You’ll need a self-hosted runner. This is because storage is limited on GH actions runners. Your scripts will fail during pre-requisite setup because they’re guaranteed to exceed GH storage quotas.
Checkout can be done with actions/checkout (with a classic PAT/ssh - I’ve been unable to get it to work with a fine grained PAT).
Building can be done with: OrchidIsle/UE5-Build-Project
I’m still in the process of working this stuff out myself, so I can’t provide much more help, but this is what I’ve gleaned so far.