chore: add model as recommended parameter for validate() (#15086)

Author: Helias

docs/source-pytorch/common/trainer.rst

@@ -164,7 +164,7 @@ or after it has already been trained.
 
 .. code-block:: python
 
-    trainer.validate(dataloaders=val_dataloaders)
+    trainer.validate(model=model, dataloaders=val_dataloaders)
 
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