Work around dead_code warning in test

    warning: field `0` is never read
       --> tests/test.rs:678:22
        |
    678 |     pub struct Tuple(u8);
        |                ----- ^^
        |                |
        |                field in this struct
        |
        = note: `#[warn(dead_code)]` on by default
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    678 |     pub struct Tuple(());
        |                      ~~

tests/test.rs

@@ -675,7 +675,7 @@ pub mod issue53 {
     use async_trait::async_trait;
 
     pub struct Unit;
-    pub struct Tuple(u8);
+    pub struct Tuple(pub u8);
     pub struct Struct {
         pub x: u8,
     }