Add missing class alias.

src/Routing/Exception/MissingControllerException.php

@@ -1,7 +1,10 @@
 <?php
 declare(strict_types=1);
 
-class_exists('Cake\Http\Exception\MissingControllerException');
+class_alias(
+    'Cake\Http\Exception\MissingControllerException',
+    'Cake\Routing\Exception\MissingControllerException',
+);
 deprecationWarning(
     'Use Cake\Http\Exception\MissingControllerException instead of Cake\Routing\Exception\MissingControllerException.'
 );