Complete the translation of rust/testing.rst and add the testing TOC entry
to rust/index.rst.
Add the translation based on commit a3b2347343
("Documentation: rust: testing: add docs on the new KUnit `#[test]` tests").
Signed-off-by: Ben Guo <benx.guo@gmail.com>
Reviewed-by: Yanteng Si <siyanteng@cqsoftware.com.cm>
Signed-off-by: Alex Shi <alexs@kernel.org>
