Skip `test_multi_gpu_data_parallel_forward` for `UperNetModelTest`
# What does this PR do?

Same as `BEIT`, this model uses some `add_module` and we need to skip this test.
_The documentation is not available anymore as the PR was closed or merged._<|||||>Wait, are you saying that models that using add_module can't leverage multi-GPU training?<|||||>> Wait, are you saying that models that using add_module can't leverage multi-GPU training?


(well, just not with the way we used in `test_multi_gpu_data_parallel_forward`, which uses `nn.DataParallel`)
(PyTorch says `It is recommended to use [DistributedDataParallel] instead)

**Partially** , that's my observation while debugging `Maskformer`, `BEIT`, and then with `LayoutLMV2`, `Data2VecVision` etc.

```
    @unittest.skip(
        reason="Data2VecVision has some layers using `add_module` which doesn't work well with `nn.DataParallel`"
    )
```

see https://github.com/huggingface/transformers/pull/17864

<|||||>@NielsRogge Let me know if you have further question :-) before giving 👍✅ . Thank you 🙏 