Fix #20513: Fix code examples in PHPDoc

framework/web/HttpException.php

@@ -18,7 +18,7 @@ use yii\base\UserException;
  *
  * Throwing an HttpException like in the following example will result in the 404 page to be displayed.
  *
- * ```php
+ * ```
  * if ($item === null) { // item does not exist
  *     throw new \yii\web\HttpException(404, 'The requested Item could not be found.');
  * }