[BUGFIX] Return ResponseInterface in ext:fluid_test action

Avoids a deprecation level log error since of this
functional test related extbase test controller action.

Resolves: #95524
Releases: master
Change-Id: Ic789f78bd96033d454da4eb94ec4da06758f7982
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71486


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/fluid/Tests/Functional/Fixtures/Extensions/fluid_test/Classes/Controller/TemplateController.php

@@ -17,15 +17,14 @@ declare(strict_types=1);
 
 namespace TYPO3Fluid\FluidTest\Controller;
 
+use Psr\Http\Message\ResponseInterface;
 use TYPO3\CMS\Extbase\Mvc\Controller\ActionController;
 
-/**
- * Class TemplateController
- */
 class TemplateController extends ActionController
 {
-    public function baseTemplateAction(): void
+    public function baseTemplateAction(): ResponseInterface
     {
         $this->view->assign('objects', ['foo']);
+        return $this->htmlResponse($this->view->render());
     }
 }