Fix validation errors in Fox.glb (#17801)

# Objective

Fix gltf validation errors in `Fox.glb`.

Inspired by #8099, but that issue doesn't appear to describe a real bug
to fix, as far as I can tell.

## Solution

Use the latest version of the Fox from
[glTF-Sample-Assets](https://github.com/KhronosGroup/glTF-Sample-Assets/blob/main/Models/Fox/glTF-Binary/Fox.glb).

## Testing

Dropped both versions in https://github.khronos.org/glTF-Validator/

`cargo run --example animated_mesh` seems to still look fine.

Before:

```
The asset contains errors.
"numErrors": 126,
"numWarnings": 4184,
```

After:

```
The asset is valid.
"numErrors": 0,
"numWarnings": 0,
```

## Discussion

The 3d testbed was panicking with
```
thread 'main' panicked at examples/testbed/3d.rs:288:60:
called `Result::unwrap()` on an `Err` value: QueryDoesNotMatch(35v1 with components Transform, GlobalTransform, Visibility, InheritedVisibility, ViewVisibility, ChildOf, Children, Name)
```
Which is bizarre. I think this might be related to #17720, or maybe the
structure of the gltf changed.

I fixed it by using updating the testbed to use a more robust method of
finding the correct entity as is done in `animated_mesh`.

CREDITS.md

@@ -32,7 +32,7 @@
 * Epic orchestra music sample, modified to loop, from [Migfus20](https://freesound.org/people/Migfus20/sounds/560449/) ([CC BY 4.0 DEED](https://creativecommons.org/licenses/by/4.0/))
 
 [MorphStressTest]: https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/MorphStressTest
-[fox]: https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/Fox
+[fox]: https://github.com/KhronosGroup/glTF-Sample-Assets/tree/main/Models/Fox
 [by PixelMannen]: https://opengameart.org/content/fox-and-shiba
 [by @tomkranis on Sketchfab]: https://sketchfab.com/models/371dea88d7e04a76af5763f2a36866bc
 [CC-BY 4.0]: https://creativecommons.org/licenses/by/4.0/

examples/testbed/3d.rs

@@ -282,19 +282,19 @@ mod animation {
         animation: Res<Animation>,
         mut players: Query<(Entity, &mut AnimationPlayer)>,
     ) {
-        let entity = children.get(trigger.target()).unwrap()[0];
-        let entity = children.get(entity).unwrap()[0];
-
-        let (entity, mut player) = players.get_mut(entity).unwrap();
-        let mut transitions = AnimationTransitions::new();
-        transitions
-            .play(&mut player, animation.animation, Duration::ZERO)
-            .seek_to(0.5)
-            .pause();
-
-        commands
-            .entity(entity)
-            .insert(AnimationGraphHandle(animation.graph.clone()))
-            .insert(transitions);
+        for child in children.iter_descendants(trigger.target()) {
+            if let Ok((entity, mut player)) = players.get_mut(child) {
+                let mut transitions = AnimationTransitions::new();
+                transitions
+                    .play(&mut player, animation.animation, Duration::ZERO)
+                    .seek_to(0.5)
+                    .pause();
+
+                commands
+                    .entity(entity)
+                    .insert(AnimationGraphHandle(animation.graph.clone()))
+                    .insert(transitions);
+            }
+        }
     }
 }