Ignore type_complexity clippy lint

    warning: very complex type used. Consider factoring parts into `type` definitions
        --> src/item.rs:1665:10
         |
    1665 |       ) -> Result<(
         |  __________^
    1666 | |         Option<(Token![&], Option<Lifetime>)>,
    1667 | |         Option<Token![mut]>,
    1668 | |         Token![self],
    1669 | |     )> {
         | |______^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
         = note: `-W clippy::type-complexity` implied by `-W clippy::all`
         = help: to override `-W clippy::all` add `#[allow(clippy::type_complexity)]`

Author: dtolnay

src/lib.rs

@@ -300,6 +300,7 @@
     clippy::too_many_arguments,
     clippy::too_many_lines,
     clippy::trivially_copy_pass_by_ref,
+    clippy::type_complexity,
     clippy::unconditional_recursion, // https://github.com/rust-lang/rust-clippy/issues/12133
     clippy::uninhabited_references,
     clippy::uninlined_format_args,