[VideoMAE] Add model to doc tests
# What does this PR do?

This PR fixes the fact that VideoMAE supports the doc tests, but wasn't actually run.

cc @ydshieh, could you point me where I need to add pip install decord to the setup of the machine that runs the doc tests?
_The documentation is not available anymore as the PR was closed or merged._<|||||>Hi @NielsRogge , it is this file to add

```
docker/transformers-all-latest-gpu/Dockerfile
```<|||||>(The image will only be built tonight)

If you want to build it now + even run the doctest to make  sure it works, let me now