Fix test ExamplesTests::test_run_translation

[ydshieh]

What does this PR do?

ExamplesTests::test_run_translation.

@gante broke this in #29600 by adding a new check

        raise ValueError(
            f"`--max_source_length` is set to {data_args.max_source_length}, but the model only has"
            f" {model.config.max_position_embeddings} position encodings. Consider either reducing"
            f" `--max_source_length` to {model.config.max_position_embeddings} or using a model with larger position "
            "embeddings"
        )

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[amyeroberts]

Thanks!