Fix doc comment (#15673)

# Objective

I noticed a weird break in a doc comment, I assume it must be a typo.

## Solution

Put the missing doc comment in there.

## Testing

It looks better in my IDE now

crates/bevy_asset/src/loader.rs

@@ -367,7 +367,7 @@ impl<'a> LoadContext<'a> {
  /// (i.to_string(), labeled.finish(Image::default(), None))
  /// }));
  /// }
-
+ ///
  /// for handle in handles {
  /// let (label, loaded_asset) = handle.join().unwrap();
  /// load_context.add_loaded_labeled_asset(label, loaded_asset);