Ignore items_after_statements pedantic clippy lint in test

warning: adding items after statements is confusing, since items exist from the start of the scope
      --> tests/test_transparent.rs:89:5
       |
    89 |     struct WithSource(#[source] io::Error);
       |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements
       = note: `-W clippy::items-after-statements` implied by `-W clippy::pedantic`
       = help: to override `-W clippy::pedantic` add `#[allow(clippy::items_after_statements)]`