[Speech2Text2] Enable tokenizers (#14390)
* [Speech2Text2] Enable tokenizers
* minor fix
* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
