[TASK] Adjust interface type hint to match current implementation (#1016

)

Currently, the actual View instance in fact doesn't always return
a string for `render()`. We should change this in the future, but
for now the interface should represent the actual
implementation.

src/View/TemplateAwareViewInterface.php

@@ -13,12 +13,14 @@
  * Optional addition to ViewInterface if the view deals with template files.
  *
  * @api
+ * @todo add return types with Fluid v5
  */
 interface TemplateAwareViewInterface
 {
     /**
+     * @todo as the outfacing interface, this (and its implementations) should actually return a string
      * @param string $templateName A template name to render, e.g. "Main/Index"
-     * @return string The rendered view
+     * @return mixed The rendered view
      * @api
      */
     public function render(string $templateName = '');