add root certs for Genoa

[Freax13]

This PR adds the root ASK/ARK certs for Genoa. I'm not sure if AMD also distributes the certificates for Genoa in the older sevcert format we use for Milan, so I used the newer x509-based certificates instead.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[Freax13]

The CI failure seems to be unrelated to this PR and already happened in previous CI runs: https://github.com/google/go-sev-guest/actions/runs/8993363579/job/24705035892.

[deeglaze]

I've updated the protoc github action in #128 so please rebase and try again. I'll work on getting it merged today.

[Freax13]

@deeglaze Now CI is failing because you haven't signed the CLA for the main E-Mail address linked to your GitHub account (i.e. the E-Mail address GitHub added a Co-authored-by tag for when I committed your suggestion).