Restore the beacon x-upstream options.disable-validation: true that was
removed during regeneration. This prevents dshackle 0.79.10's beacon health
validator from timing out on the spec-compliant empty-body 200 that nimbus
returns, causing the upstream to flap UNAVAILABLE. Matches the established
ethereum-beacon pattern.
Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>