bug fix; processing real stereo data

while processing real stereo data we do not have the true shower id in the batch

dl1_data_handler/loader.py

@@ -149,7 +149,10 @@ def __getitem__(self, index):
                 )
         elif self.DLDataReader.mode == "stereo":
             batch = self.DLDataReader.generate_stereo_batch(batch_indices)
-            batch_grouped = batch.group_by(["obs_id", "event_id", "tel_type_id", "true_shower_primary_class"])
+            if self.DLDataReader.process_type == ProcessType.Simulation:
+                batch_grouped = batch.group_by(["obs_id", "event_id", "tel_type_id", "true_shower_primary_class"])
+            elif self.DLDataReader.process_type == ProcessType.Observation:
+                batch_grouped = batch.group_by(["obs_id", "event_id", "tel_type_id"])
             features = []
             true_shower_primary_class = []
             log_true_energy = []