`image-segmentation` pipeline: re-enable `small_model_pt` test.
Author: Narsil
Pull request: yes

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

I re-enable this tests, as it should work.

The error @alaradirik was seeing, seems to not happen on main, and the results are actually deterministic.

However 
`semantic` returns 3 different masks
`panoptic` returns 0 masks

The old tests used to be `panoptic` and would return `2` masks (probably because of thresholding) of `Label_215`.

I kept the old values since I think something is wrong currently, but I wanted to re-enable the test before doing any modification to the actual pipeline code.
https://github.com/huggingface/transformers/pull/19727/files

@ydshieh I pinged you to see if you had better ideas to make tests less sensitive to the `Pillow` version. (there was a difference between CI and my computer), a few different pixels, and totally different hash.

We could use `white_pixel_proportion` instead and let the precision handle the slight differences in `Pillow` version, but I fear we're going to miss some really bad changes (when the actual shape of the mask is totally modified), that's why we added the `hash` in the first place. (But it seems to be quite sensitive, not flaky, but still seemed it could be painful to keep track of this)


I will check this pipeline to get a better idea of it, and see if I have any idea 👀 👀 
                                                                                                                         👀 👀 !