gltf: do not import IoTaskPool in wasm (#5038)

# Objective

- Remove a warning when building for wasm

## Solution

- Do not import the dependency when building for wasm

crates/bevy_gltf/src/loader.rs

@@ -29,6 +29,7 @@ use bevy_render::{
     view::VisibleEntities,
 };
 use bevy_scene::Scene;
+#[cfg(not(target_arch = "wasm32"))]
 use bevy_tasks::IoTaskPool;
 use bevy_transform::{components::Transform, TransformBundle};