[Clippy] Swap unnecessary_owned_empty_strings to use diagnostic item instead of path

Author: GnomedDev

alloc/src/string.rs

@@ -440,6 +440,7 @@ impl String {
     /// ```
     #[inline]
     #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_new")]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     pub const fn new() -> String {