Convert conservative_impl_trait.rs to compile-pass

src/test/run-pass/traits/conservative_impl_trait.stderr

@@ -1,8 +0,0 @@
-warning: function is never used: `batches`
-  --> $DIR/conservative_impl_trait.rs:14:1
-   |
-LL | fn batches(n: &u32) -> impl Iterator<Item=&u32> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: #[warn(dead_code)] on by default
-

src/test/ui/traits/conservative_impl_trait.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// run-pass
+// compile-pass
 // #39665
 
 fn batches(n: &u32) -> impl Iterator<Item=&u32> {