message: Fix misleading error.
diff: @@ -205,7 +205,7 @@ where
  match self.get(correlation_id, &key).map_err(Into::into)? {
  Some(StoredValue::ContractWasm(contract_wasm)) => Ok(contract_wasm),
  Some(other) => Err(execution::Error::TypeMismatch(
  - StoredValueTypeMismatch::new("ContractHeader".to_string(), other.type_name()),
  + StoredValueTypeMismatch::new("ContractWasm".to_string(), other.type_name()),
  )),
  None => Err(execution::Error::KeyNotFound(key)),
  }
  