[Clippy] Add vec_reserve & vecdeque_reserve diagnostic items

Author: wowinter13

alloc/src/collections/vec_deque/mod.rs

@@ -823,6 +823,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// assert!(buf.capacity() >= 11);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vecdeque_reserve")]
     #[track_caller]
     pub fn reserve(&mut self, additional: usize) {
         let new_cap = self.len.checked_add(additional).expect("capacity overflow");

alloc/src/vec/mod.rs

@@ -1267,6 +1267,7 @@ impl<T, A: Allocator> Vec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[track_caller]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_reserve")]
     pub fn reserve(&mut self, additional: usize) {
         self.buf.reserve(self.len, additional);
     }