Modify group_sub_entities in TokenClassification Pipeline to support label with "-"

[eshoyuan]

What does this PR do?

This PR provides a bug fix for the group_sub_entities function within the NER pipeline. Previously, the function split entities on every dash (-), which led to incorrect parsing of entities that inherently contain a dash in their names. The code change ensures that only the first dash is considered for splitting, preserving the integrity of the entity names.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Who can review?

• pipelines: @Narsil

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[Narsil]

LGTM.

@amyeroberts for core maintainer's opinion

[amyeroberts]

LGTM too - thanks for adapting!