Update RectAreaLight.html (#27441)

Fix a error

docs/api/zh/lights/RectAreaLight.html

@@ -33,7 +33,7 @@
 		rectLight.lookAt( 0, 0, 0 );
 		scene.add( rectLight )
 
-		rectLightHelper = new RectAreaLightHelper( rectLight );
+		const rectLightHelper = new RectAreaLightHelper( rectLight );
 		scene.add( rectLightHelper );
 		</code>