code: def validation_step(self, val_batch, batch_idx):
      x, y = val_batch
      logits = self.forward(x)
      loss = F.nll_loss(logits, y)
      acc = self.accuracy(logits, y)
      self.val_acc_list.append(acc)
      self.val_loss_list.append(loss)
      return {"val_loss": loss, "val_accuracy": acc}
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  from torch.utils.data import DataLoader
  from torchmetrics import Accuracy
  from ray import train
  from ray.train.lightning._lightning_utils import import_lightning
label_desc: Use image node_id 5 for calling the LightningMNISTClassifier obj's underlying member method code with example usage: obj.validation_step(val_batch, batch_idx) and returns: dict