Fix animate_scale scaling z value in text2d example (bevyengine#9769)

# Objective

I noticed this while testing bevyengine#9733.

It's not causing any problems, but we shouldn't teach users to scale 2d
stuff in z.

## Solution

Only scale in x and y.

examples/2d/text2d.rs

@@ -187,6 +187,9 @@ fn animate_scale(
  // rendered quad, resulting in a pixellated look.
  for mut transform in &mut query {
  transform.translation = Vec3::new(400.0, 0.0, 0.0);
- transform.scale = Vec3::splat((time.elapsed_seconds().sin() + 1.1) * 2.0);
+
+ let scale = (time.elapsed_seconds().sin() + 1.1) * 2.0;
+ transform.scale.x = scale;
+ transform.scale.y = scale;
  }
 }