[DOCTEST] Fix the documentation of RoCBert
# What does this PR do?
Fixes the documetnation test

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20142). All of your documentation changes will be reflected on that endpoint.<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20142). All of your documentation changes will be reflected on that endpoint.<|||||>Sorry for the late fix, tests are passing locally. <|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20142). All of your documentation changes will be reflected on that endpoint.