Use advance_by instead of nth in Skip::next

Combined with the `iter::Cloned::advance_by` implementation this leads to fewer clone operations

Author: the8472

library/core/src/iter/adapters/skip.rs

@@ -33,7 +33,7 @@ where
     #[inline]
     fn next(&mut self) -> Option<I::Item> {
         if unlikely(self.n > 0) {
-            self.iter.nth(crate::mem::take(&mut self.n) - 1);
+            let _ = self.iter.advance_by(crate::mem::take(&mut self.n));
         }
         self.iter.next()
     }