process: Tweak drop_kills test

tests/stdio.rs

@@ -101,10 +101,9 @@ fn drop_kills() {
     let stdout = child.stdout().take().unwrap();
     drop(child);
 
+    drop(lp.run(write_all(stdin, b"1234")));
     let (_, output) = lp.run(read_to_end(stdout, Vec::new())).unwrap();
     assert_eq!(output.len(), 0);
-    let err = lp.run(write_all(stdin, b"1234")).err().unwrap();
-    assert_eq!(err.kind(), io::ErrorKind::BrokenPipe);
 }
 
 #[test]