using_cxx crate_universe example fails clippy

[UebelAndre]

When using Rust 1.81.0 the cxx example fails with the following clippy error.

cd examples/crate_universe
bazel build //using_cxx/... --config=clippy

error: `?Sized` bound is ignored because of a `Sized` requirement
  --> using_cxx/src/main.rs:11:14
   |
11 |         type MultiBuf;
   |              ^^^^^^^^^
   |
note: `T` cannot be unsized because of the bound
  --> using_cxx/src/main.rs:11:9
   |
11 |         type MultiBuf;
   |         ^^^^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_maybe_sized
   = note: `-D clippy::needless-maybe-sized` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::needless_maybe_sized)]`
help: change the bounds that require `Sized`, or remove the `?Sized` bound
   |
11 -         type MultiBuf;
   |
error: aborting due to 1 previous error