fix(phpstan): correct variable type

Related: #4

phpstan-baseline.neon

 parameters:
 	ignoreErrors:
-		-
-			message: "#^Parameter \\#2 \\$val of method QUI\\\\QDOM\\:\\:setAttribute\\(\\) expects array\\|bool\\|object\\|string, int given\\.$#"
-			count: 1
-			path: src/QUI/Interview/Controls/IntervieweeData.php

src/QUI/Interview/Controls/IntervieweeData.php

@@ -35,7 +35,7 @@ public function __construct($attributes = [])
 
         parent::__construct($attributes);
 
-        $this->setAttribute('cacheable', 0);
+        $this->setAttribute('cacheable', "0");
     }
 
     /**
@@ -43,7 +43,7 @@ public function __construct($attributes = [])
      *
      * @see \QUI\Control::create()
      */
-    public function getBody()
+    public function getBody(): string
     {
         $Engine = QUI::getTemplateManager()->getEngine();
         $Site   = $this->getSite();