add exception for liballoc benches to tidy
add exception for liballoc benches to tidy

Signed-off-by: Nell Shamrell <8ca9739a2537c8ebcbfe176c51c6e5e22618bd2f@gmail.com>

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust