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>

compose_registry.json

@@ -8389,23 +8389,6 @@
       "polygon-mainnet-bor-archive-pebble-path"
     ]
   },
-  {
-    "chain": "mainnet",
-    "client": "bor",
-    "compose_file": "polygon/bor/polygon-mainnet-bor-minimal-pebble-path",
-    "features": [
-      "path",
-      "pebble"
-    ],
-    "network": "polygon",
-    "node": null,
-    "relay": null,
-    "stack": null,
-    "type": "minimal",
-    "volumes": [
-      "polygon-mainnet-bor-minimal-pebble-path"
-    ]
-  },
   {
     "chain": "mainnet",
     "client": "bor",