[Clippy] Swap manual_strip to use diagnostic items instead of paths

Author: GnomedDev

Diff for: core/src/str/mod.rs

@@ -134,6 +134,7 @@ impl str {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_str_len", since = "1.39.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "str_len")]
     #[must_use]
     #[inline]
     pub const fn len(&self) -> usize {
@@ -1157,6 +1158,7 @@ impl str {
     /// assert!(bananas.starts_with(&['a', 'b', 'c', 'd']));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "str_starts_with")]
     pub fn starts_with<P: Pattern>(&self, pat: P) -> bool {
         pat.is_prefix_of(self)
     }
@@ -1181,6 +1183,7 @@ impl str {
     /// assert!(!bananas.ends_with("nana"));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "str_ends_with")]
     pub fn ends_with<P: Pattern>(&self, pat: P) -> bool
     where
         for<'a> P::Searcher<'a>: ReverseSearcher<'a>,