fix: ensure newline at end of file in useless_conversion test

Author: keirsalterego

tests/ui/useless_conversion_into_iter_adjustments.rs

@@ -1,5 +1,5 @@
 #![warn(clippy::useless_conversion)]
-#![allow(clippy::into_iter_on_ref)] 
+#![allow(clippy::into_iter_on_ref)]
 fn consume_iter<'a, I>(_: I)
 where
     I: IntoIterator<Item = &'a i32>,
@@ -11,4 +11,4 @@ fn main() {
     let items = &&[1, 2, 3];
     consume_iter(items.into_iter());
     //~^ useless_conversion
-}
+}