`IndexError: tuple index out of range` in `input_ids` during pre-training

Following the [instructions](https://github.com/AnswerDotAI/ModernBERT?tab=readme-ov-file#setup) in the README, I am working on pre-training from scratch. I ran training with the composer framework using the `yamls/main/flex-bert-base.yaml` config and with the c4 dataset `./my-copy-c4`.
[note that I verified that the dataloader works fine following the [instructions](https://github.com/mosaicml/examples/tree/main/examples/benchmarks/bert#test-the-dataloader).]

However, I encountered the following error during training:

```
IndexError: tuple index out of range

File "/.../ModernBERT/src/bert_layers/embeddings.py", line 153, in forward
position_ids = self.position_ids[:, 0 : input_ids.shape[1]]
~~~~~~~~~~~~~~~^^^
```

## Steps to Reproduce

1. Prepare the c4 dataset.
2. Set up the conda environment per instructions.
3. Run training with `composer main.py yamls/main/flex-bert-base.yaml`
4. The error occurs during training in `bert_layers/embeddings.py`