fix: serde rename camle case for execution payload body (#5846)

Author: mattsse

beacon_node/execution_layer/src/engine_api/json_structures.rs

@@ -720,6 +720,7 @@ impl From<ForkchoiceUpdatedResponse> for JsonForkchoiceUpdatedV1Response {
 
 #[derive(Clone, Debug, Serialize, Deserialize)]
 #[serde(bound = "E: EthSpec")]
+#[serde(rename_all = "camelCase")]
 pub struct JsonExecutionPayloadBodyV1<E: EthSpec> {
     #[serde(with = "ssz_types::serde_utils::list_of_hex_var_list")]
     pub transactions: Transactions<E>,