[Doctests] Fix all T5 doc tests (#16646)
* [Doctests] Fix all T5 doc tests
* make style
* Update docs/source/en/model_doc/t5.mdx
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
* Apply Sylvains comments
* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
