Nested subasset loads tries to return the root nested asset.

## Bevy version

[ab0e3f8](https://github.com/bevyengine/bevy/commit/ab0e3f871452f6be5c99f18175a8949b8a19e2dd)

---

In an asset loader, do a nested immediate asset load where the path you provide is a subasset:

```rust
// This returns a type mismatch error since Gltf (the type of `some_asset.gltf`) does not match `Mesh`.
load_context.loader().immediate().load("some_asset.gltf#Mesh0/Primitive0").await;
```

This means if the type of a subasset matched the root asset, we would unknowingly be using the wrong asset!