Fix NNTemplateCore callback to always inject the metadata

Author: lucmos

src/nn_core/callbacks.py

@@ -51,7 +51,7 @@ def on_train_end(self, trainer: pl.Trainer, pl_module: pl.LightningModule) -> No
     def on_save_checkpoint(
         self, trainer: pl.Trainer, pl_module: pl.LightningModule, checkpoint: Dict[str, Any]
     ) -> None:
-        if self._is_nnlogger(trainer):
+        if trainer.logger is not None:
             trainer.logger.on_save_checkpoint(trainer=trainer, pl_module=pl_module, checkpoint=checkpoint)
             metadata = getattr(trainer.datamodule, "metadata", None)
             if metadata is not None: