[BUG]: `DataCollatorForSupervisedDataset` in sft_dataset.py not support left padding

[Desperado-Jia]

🐛 Describe the bug

def __call__(self, instances: Sequence[Dict]) -> Dict[str, torch.Tensor]:
    input_ids, labels = tuple([instance[key] for instance in instances] for key in ("input_ids", "labels"))
    input_ids = torch.nn.utils.rnn.pad_sequence(input_ids,
                                                batch_first=True,
                                                padding_value=self.tokenizer.pad_token_id)
    labels = torch.nn.utils.rnn.pad_sequence(labels, batch_first=True, padding_value=IGNORE_INDEX)
    return dict(
        input_ids=input_ids,
        labels=labels,
        attention_mask=input_ids.ne(self.tokenizer.pad_token_id),
    )

This function not support left padding (e.g., BLOOM)

Environment

No response