🐛 fix: fix reward model train seq_cls (#3921)

Author: gaohongkui

swift/llm/model/register.py

@@ -230,6 +230,11 @@ def get_model_tokenizer_from_local(model_dir: str,
         if model is None:
             if model_info.task_type == 'seq_cls' and not model_meta.is_reward:
                 context = partial(patch_automodel_for_sequence_classification, model_meta=model_meta)
+            elif model_info.task_type == 'seq_cls' and model_meta.is_reward and model_config.num_labels > 1:
+                logger.warning('You are using a reward model for seq_cls task and num_labels > 1, '
+                               'ignore_mismatched_sizes will be set to True')
+                model_kwargs['ignore_mismatched_sizes'] = True
+                context = partial(patch_automodel_for_sequence_classification, model_meta=model_meta)
             else:
                 context = partial(patch_automodel, automodel_class=automodel_class, model_info=model_info)
             with context():