Fix internal rustdoc broken links

As it was suggested in #81037 `SpecFromIter` is not
in the scope and therefore (even it should fail),
we get a warning when we try do document private
intems in `rust/library/alloc/`.

This fixes #81037 by adding the trait in the scope
and also adding an `allow(unused_imports)` flag so that
the compiler does not complain, Since the trait is not used
per se in the code, it's just needed to have properly documented
docs.

0 files changed, 0 insertions, 0 deletions