Fix docstring example for select_columns in IterableDatasetDict

[albertvillanova]

Fix docstring example for select_columns in IterableDatasetDict.

This PR updates the usage example for selecting columns in a streaming dataset. The example now correctly uses the select_columns method instead of the outdated select method.

Changes

• Documentation update:
  • Updated the example in the docstring of select_columns in dataset_dict.py to use select_columns("text") instead of the deprecated select("text").

[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.