Update tests/pass/move-data-across-await-point.rs

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: bryangarza

tests/pass/move-data-across-await-point.rs

@@ -25,6 +25,7 @@ async fn helper_async(mut data: Vec<u8>, raw_pointer: *mut Vec<u8>) {
     // here should be equal.
     assert_ne!(raw_pointer, raw_pointer2);
     unsafe {
+        // This writes into the `x` in `data_moved_async`, re-initializing it.
         std::ptr::write(raw_pointer, vec![3]);
     }
 }