Fix CI warning (Handle<Image>).

crates/bevy_pbr/src/pbr_material.rs

@@ -395,7 +395,7 @@ pub struct StandardMaterial {
     /// # use bevy_image::ImageLoaderSettings;
     /// #
     /// fn load_normal_map(asset_server: Res<AssetServer>) {
-    ///     let normal_handle = asset_server.load_with_settings(
+    ///     let normal_handle: Handle<Image> = asset_server.load_with_settings(
     ///         "textures/parallax_example/cube_normal.png",
     ///         // The normal map texture is in linear color space. Lighting won't look correct
     ///         // if `is_srgb` is `true`, which is the default.