[WIP] Fix ImageSegmentationPipeline
# What does this PR do?
- Fixes the ImageSegmentationPipeline test errors caused by a `[recent PR](https://github.com/huggingface/transformers/pull/19205)` that adds new post-processing methods to DETR. 

The following PRs will need to be merged first to ensure DETR and MaskFormer have consistent `post_process_panoptic_segmentation` and `post_process_semantic_segmentation outputs `:
- https://github.com/huggingface/transformers/pull/19172
- https://github.com/huggingface/transformers/pull/19262

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ X] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ X] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
     This issue fixes a pipeline error caused by recent changes to image segmentation post-processing methods of DETR.
     https://github.com/huggingface/transformers/pull/19248
- [X ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_19264). All of your documentation changes will be reflected on that endpoint.<|||||>The issues addressed by this PR are fixed in this [PR](https://github.com/huggingface/transformers/pull/19367).