[TASK] Replace deprecated childNodes ViewHelper property

`AbstractViewHelper::$childNodes` is deprecated and will  be
removed with Fluid v5.

Original change in Fluid: TYPO3/Fluid#1091

Resolves: #106792
Releases: main, 13.4
Change-Id: I9aec7b161f287ecbafe461b327141bb8083d1ee4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/89571
Reviewed-by: Simon Praetorius <[email protected]>
Reviewed-by: Christian Kuhn <[email protected]>
Tested-by: Stefan Bürk <[email protected]>
Tested-by: core-ci <[email protected]>
Reviewed-by: Stefan Bürk <[email protected]>
Tested-by: Simon Praetorius <[email protected]>
Tested-by: Christian Kuhn <[email protected]>

Author: s2b

Classes/ViewHelpers/Be/Menus/ActionMenuItemGroupViewHelper.php

@@ -57,7 +57,7 @@ public function render(): string
     {
         $this->tag->addAttribute('label', $this->arguments['label']);
         $options = '';
-        foreach ($this->childNodes as $childNode) {
+        foreach ($this->viewHelperNode->getChildNodes() as $childNode) {
             if ($childNode instanceof ViewHelperNode) {
                 $options .= $childNode->evaluate($this->renderingContext);
             }

Classes/ViewHelpers/Be/Menus/ActionMenuViewHelper.php

@@ -58,7 +58,7 @@ public function initializeArguments(): void
     public function render(): string
     {
         $options = '';
-        foreach ($this->childNodes as $childNode) {
+        foreach ($this->viewHelperNode->getChildNodes() as $childNode) {
             if ($childNode instanceof ViewHelperNode) {
                 $options .= $childNode->evaluate($this->renderingContext);
             }