beacon x-upstreams: restore disable-validation: true for gnosis and ethereum nimbus beacon-chain upstreams

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>

ethereum/reth/ethereum-sepolia-reth-archive-trace--nimbus.yml

@@ -183,6 +183,12 @@ x-upstreams:
     chain: eth-beacon-chain-sepolia
     labels:
       provider: $${PROVIDER}-beacon-chain
+    options:
+      # dshackle 0.79.10's beacon health validator times out on the spec-compliant
+      # empty-body 200 from /eth/v1/node/health (nimbus), flapping the upstream
+      # UNAVAILABLE and failing live requests ("Source was empty"). Head tracking
+      # still governs health with validation off. 2026-07-10, dRPC incident.
+      disable-validation: true
     connection:
       generic:
         rpc: