GHA can do nested virt via KVM. Here is an action that runs a test that boots up a VM running NixOS: https://github.com/aksiksi/compose2nix/blob/main/.github/wor...

You can also run QEMU if you want to build for ARM (although this announcement makes this unnecessary): https://github.com/aksiksi/ncdmv/blob/aa108a1c1e2c14a13dfbc0...