POST /eth/v2/beacon/pool/attestations bugfixes (#6867)

validator_client/validator_services/Cargo.toml

@@ -8,6 +8,7 @@ authors = ["Sigma Prime <contact@sigmaprime.io>"]
 beacon_node_fallback = { workspace = true }
 bls =  { workspace = true }
 doppelganger_service = { workspace = true }
+either = { workspace = true }
 environment = { workspace = true }
 eth2 = { workspace = true }
 futures = { workspace = true }