Resolve manual_string_new pedantic clippy lint

warning: empty String is being created manually
        --> test_suite/tests/test_annotations.rs:2280:29
         |
    2280 |     let data = Data::C { t: "".to_string() };
         |                             ^^^^^^^^^^^^^^ help: consider using: `String::new()`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_string_new
         = note: `-W clippy::manual-string-new` implied by `-W clippy::pedantic`

test_suite/tests/test_annotations.rs

@@ -2277,7 +2277,7 @@ fn test_internally_tagged_enum_with_skipped_conflict() {
         },
     }
 
-    let data = Data::C { t: "".to_string() };
+    let data = Data::C { t: String::new() };
 
     assert_tokens(
         &data,