fix: select correct gossip type when publishing single attestation (#7256)

* fix: select correct gossip type when publishing single attestation

* Add SingleAttestation as alias to phase0 ssz types

Author: nflaig

packages/beacon-node/src/network/gossip/topic.ts

@@ -89,7 +89,7 @@ export function getGossipSSZType(topic: GossipTopic) {
     case GossipType.beacon_aggregate_and_proof:
       return sszTypesFor(topic.fork).SignedAggregateAndProof;
     case GossipType.beacon_attestation:
-      return sszTypesFor(topic.fork).Attestation;
+      return sszTypesFor(topic.fork).SingleAttestation;
     case GossipType.proposer_slashing:
       return ssz.phase0.ProposerSlashing;
     case GossipType.attester_slashing:

packages/types/src/phase0/sszTypes.ts

@@ -316,6 +316,8 @@ export const Attestation = new ContainerType(
   {typeName: "Attestation", jsonCase: "eth2"}
 );
 
+export const SingleAttestation = Attestation;
+
 export const AttesterSlashing = new ContainerType(
   {
     // In state transition, AttesterSlashing attestations are only partially validated. Their slot and epoch could