docs: fix test classname

Author: kenjis

user_guide_src/source/testing/controllers/002.php

@@ -6,7 +6,7 @@
 use CodeIgniter\Test\ControllerTestTrait;
 use CodeIgniter\Test\DatabaseTestTrait;
 
-class FooControllerTest extends CIUnitTestCase
+class ForumControllerTest extends CIUnitTestCase
 {
     use ControllerTestTrait;
     use DatabaseTestTrait;