Fix warning for MCTC model
# What does this PR do?

In #20861, the warning introduced did not use the right direction for the test. This PR fixes that.
Fixes #21031
Merging to fix the warning @ydshieh but can address any comment in a later PR :-) <|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21049). All of your documentation changes will be reflected on that endpoint.