beacon x-upstreams: disable-validation on all beacon-chain upstreams

dshackle 0.79.10's beacon health validator (GET /eth/v1/node/health via
GenericSingleCallValidator) times out after 5000ms on the spec-compliant
empty-body 200 that nimbus returns, marking the upstream UNAVAILABLE in a
flap loop; live requests routed during flap windows fail 'Source was empty'.
This is the root cause behind dRPC's 617k failed validators POSTs complaint
(2026-07-09). Reproduced + workaround verified on an isolated dshackle
instance on de-14. Head tracking still governs availability.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ethereum/besu/ethereum-mainnet-besu-pruned-bonsai--nimbus.yml

@@ -189,6 +189,12 @@ x-upstreams:
     chain: eth-beacon-chain
     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: