Ignore `test_multi_gpu_data_parallel_forward` for `LayoutLMV2`
# What does this PR do?

Ignore test_multi_gpu_data_parallel_forward for LayoutLMV2.

The reason to skip is the same as in #17864. (The usage of `add_module`)
_The documentation is not available anymore as the PR was closed or merged._<|||||>Ok, so it's always advised to avoid using `add_module`?<|||||>@NielsRogge Not really. The test `test_multi_gpu_data_parallel_forward` uses `nn.DataParallel`, but PyTorch recommendes to use `DistributedDataParallel`, see [here](https://pytorch.org/docs/stable/generated/torch.nn.DataParallel.html`.)

However, I don't know if `add_module` works well with `DistributedDataParallel`. It would be good to avoid `add_module` until we decide to remove all `nn.DataParallel`. But in the cases where you really need `add_module`, don't hesitate.<|||||>@NielsRogge I guess I need to add more meaningful commit message, so you don't have to double check when clicking the merge button :-)