Fix fine-tuning callback test (#5643)

* fix

* batch size

Author: awaelchli

tests/helpers/boring_model.py

@@ -96,7 +96,7 @@ def step(self, x):
         return out
 
     def training_step(self, batch, batch_idx):
-        output = self.layer(batch)
+        output = self(batch)
         loss = self.loss(batch, output)
         return {"loss": loss}
 
@@ -107,15 +107,15 @@ def training_epoch_end(self, outputs) -> None:
         torch.stack([x["loss"] for x in outputs]).mean()
 
     def validation_step(self, batch, batch_idx):
-        output = self.layer(batch)
+        output = self(batch)
         loss = self.loss(batch, output)
         return {"x": loss}
 
     def validation_epoch_end(self, outputs) -> None:
         torch.stack([x['x'] for x in outputs]).mean()
 
     def test_step(self, batch, batch_idx):
-        output = self.layer(batch)
+        output = self(batch)
         loss = self.loss(batch, output)
         return {"y": loss}