fix uncaught init of linear layer in clip's/siglip's for image classification models
Author: vasqu
Pull request: yes
Labels: name: single-model-run-slow

# What does this PR do?
Fixes the uncaught initialisation of the last linear layer in `ForImageClassification` of Clip/Siglip, especially when using `from_pretrained`. More in-depth discussion at #30374. Possible failing tests are equivalence tests between tf/pt/flax; seems unrelated. 

The remaining discrepancy between `from_pretrained` and "from_config" has yet to be resolved. I'll leave it out since it might imply bigger things than reflected here. 


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Fixes #30374


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Comments:
LGTM!

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_30435). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

@vasqu Could you push an empty commit to this branch? This should trigger the slow model tests to make sure everything's still working as expected for CLIP 

@amyeroberts pushed an empty commit, but seems like the slow test still hasn't been triggered. 

Oh might've been that it's just slow :sweat_smile: my bad

@vasqu Slow by name, slow by nature ;) I think it was actually waiting for me to approve - it won't run automatically for non-repo maintainers for security and to save our CI as they're quite heavy tests 

Ah, I see. Makes sense and yea, the name should've rang a bell ^^ 

Thanks again for fixing this!