Fix pipeline tests for Roberta-like tokenizers
# What does this PR do?

The pipeline tests rely on an inheritance test for the (weird) behavior of Roberta-like models/tokenizers having a +2 / -2 on the embeddings. This was working fine until someone decided to encourage the community to uncouple all configs, and now it breaks.

This PR fixes it.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_19365). All of your documentation changes will be reflected on that endpoint.