[libs.common.engine.callbacks] Fix access to last learning-rate

src/mednet/libs/common/engine/callbacks.py

@@ -147,7 +147,7 @@ class LoggingCallback(lightning.pytorch.Callback):
         else:
             self._to_log["learning-rate"] = pl_module.trainer.lr_scheduler_configs[
                 0
-            ].scheduler.get_last_lr()  # type: ignore
+            ].scheduler.get_last_lr()[0]  # type: ignore
 
         overall_cycle_time = time.time() - self._start_training_epoch_time
         self._to_log["cycle-time-seconds/train"] = overall_cycle_time