Spanish Docs - fix gendered sentence
# What does this PR do?
Fixes a gendered sentence in [es/index.mdx](https://github.com/huggingface/transformers/blob/main/docs/source/es/index.mdx).

## Notes
FYI @osanseviero, I believe this was the sentence that was still gendered in the Spanish docs :)
_The documentation is not available anymore as the PR was closed or merged._