Examples: Fix shadow map enabled in `webgpu_shadowmap` (#29520)

examples/webgpu_shadowmap.html

@@ -174,6 +174,7 @@
 				renderer.setPixelRatio( window.devicePixelRatio );
 				renderer.setSize( window.innerWidth, window.innerHeight );
 				renderer.setAnimationLoop( animate );
+				renderer.shadowMap.enabled = true;
 				renderer.toneMapping = THREE.ACESFilmicToneMapping;
 				document.body.appendChild( renderer.domElement );