fix: Fix return types in tests.

src/Bundle/ChillDocGeneratorBundle/tests/Service/Context/BaseContextDataTest.php

@@ -23,7 +23,7 @@ use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
  */
 final class BaseContextDataTest extends KernelTestCase
 {
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
         self::bootKernel();