Fix clippy::needless_return warning in test

```
warning: unneeded `return` statement
  --> tests/std.rs:80:5
   |
80 |     return ret;
   |     ^^^^^^^^^^^ help: remove `return`: `ret`
   |
   = note: `#[warn(clippy::needless_return)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
```

tests/std.rs

@@ -76,7 +76,7 @@ pub async fn run_output(mut cmd: Command) -> String {
         .await
         .unwrap();
     assert!(p.status().await.unwrap().success());
-    return ret;
+    ret
 }
 
 #[test]