Examples: Fixed NodeMaterial not import error. (#25400)

examples/webgl_nodes_loader_gltf_sheen.html

@@ -36,6 +36,8 @@
 
 			import * as THREE from 'three';
 
+			import { NodeMaterial, uv, mul, mix, color, checker } from 'three/nodes';
+
 			import { nodeFrame } from 'three/addons/renderers/webgl/nodes/WebGLNodes.js';
 
 			import { OrbitControls } from 'three/addons/controls/OrbitControls.js';