[BUGFIX] Prevent deprecation notice in InputLinkElement

Add missing typecast to prevent deprecation notice.

Resolves: #102396
Releases: 11.5
Change-Id: I49f22bac872b2485cb282ce26121a06e08f87810
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81802
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>

typo3/sysext/backend/Classes/Form/Element/InputLinkElement.php

@@ -228,7 +228,7 @@ public function render()
         $expansionHtml[] =              '<button class="btn btn-default t3js-form-field-inputlink-explanation-toggle" type="button" title="' . htmlspecialchars($toggleButtonTitle) . '">';
         $expansionHtml[] =                  $this->iconFactory->getIcon('actions-version-workspaces-preview-link', Icon::SIZE_SMALL)->render();
         $expansionHtml[] =              '</button>';
-        $expansionHtml[] =              '<input type="hidden" name="' . $parameterArray['itemFormElName'] . '" value="' . htmlspecialchars($itemValue) . '" />';
+        $expansionHtml[] =              '<input type="hidden" name="' . $parameterArray['itemFormElName'] . '" value="' . htmlspecialchars((string)$itemValue) . '" />';
         $expansionHtml[] =          '</div>';
         $expansionHtml[] =      '</div>';
         if (!empty($valuePickerHtml) || !empty($fieldControlHtml)) {