Fix needless_borrow clippy lint in new control character test

    warning: this expression creates a reference which is immediately dereferenced by the compiler
        --> tests/test.rs:2515:9
         |
    2515 |         &"\"\t\n\r\"",
         |         ^^^^^^^^^^^^^ help: change this to: `"\"\t\n\r\""`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
         = note: `-W clippy::needless-borrow` implied by `-W clippy::all`
         = help: to override `-W clippy::all` add `#[allow(clippy::needless_borrow)]`

tests/test.rs

@@ -2512,7 +2512,7 @@ fn test_control_character_search() {
 
     // Multiple occurrences
     test_parse_err::<String>(&[(
-        &"\"\t\n\r\"",
+        "\"\t\n\r\"",
         "control character (\\u0000-\\u001F) found while parsing a string at line 1 column 2",
     )]);
 }