Fix the weight name in GTEClassificationHead

[kozistr]

What does this PR do?

Fixes #605

The pooler layer loads its weight using an incorrect key name, causing the classifier and reranker based on GTE to produce wrong outputs.

changelog

• load the weight from new.pooler.dense.* or pooler.dense.*
• add the tests
• update the flash gte test

tests

I've checked that the outputs are aligned with the HF models.

• WebOrganizer/FormatClassifier
• Alibaba-NLP/gte-multilingual-reranker-base

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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@Narsil @alvarobartt

[Narsil]

LGTM

[WissamAntoun]

Thank you!