Fix auto_exposure example (#15827)

# Objective

Fixes #15824

## Solution

Looks like this was just a goof in migrating the example itself.

Added back in the rotation component of the transform that got dropped.

## Testing

`cargo run --example auto_exposure`

examples/3d/auto_exposure.rs

@@ -96,7 +96,7 @@ fn setup(
                     ),
                     ..default()
                 })),
-                Transform::from_translation(side * 2.0 + height),
+                Transform::from_translation(side * 2.0 + height).looking_at(height, Vec3::Y),
             ));
         }
     }