Update translation requests contact (#18941)
* Update TRANSLATING.md
Update the contact to @GuggerSylvain
* Update docs/TRANSLATING.md
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
