WCAG not complied in navigation panel administration

This is a continuation of XWIKI-2904 which has been partially solved.

```
WCAG fails in the test class [org.xwiki.panels.test.ui.docker.AllIT]:
__________
Validation in the test method [verifyPanelCaching]
Check for [org.xwiki.panels.test.po.NavigationPanelAdministrationPage] at http://xwikiweb:8080/xwiki/bin/admin/XWiki/XWikiPreferences?form_token=MDyIPXPlyu0M6tkNYcRvEg&editor=globaladmin&forceEdit=true&section=panels.navigation&force=true&.
Found [2] items

1: Certain ARIA roles must contain particular children
Description: Ensure elements with an ARIA role that require child roles contain them
Help URL: https://dequeuniversity.com/rules/axe/4.10/aria-required-children?application=axeAPI
Help: Certain ARIA roles must contain particular children
Impact: critical
Tags: cat.aria, wcag2a, wcag131, EN-301-549, EN-9.1.3.1

HTML element:
<div class="xtree jstree-no-links jstree-xwiki-large jstree jstree-1 jstree-xwiki jstree-xwiki-responsive" data-responsive="true" data-url="/xwiki/bin/get/Panels/Navigation?outputSyntax=plain&sheet=XWiki.DocumentTree&showAttachments=false&showTranslations=false&exclusions=space%3ACarol&exclusions=space%3AIconThemesCode&exclusions=space%3APanels&exclusions=space%3APanelsCode&exclusions=space%3AIndex&exclusions=space%3AAppWithinMinutes&exclusions=space%3AAttachment&exclusions=space%3AIconThemes" data-draganddrop="true" data-contextmenu="false" data-icons="false" data-edges="false" data-checkboxes="false" data-opento="document:xwiki:Panels.Navigation" data-finder="false" role="tree" aria-multiselectable="true" tabindex="0" aria-activedescendant="document:xwiki:A AA.WebHome" aria-busy="false">
Selector: [.jstree-no-links]
Fix any of the following:
Element has children which are not allowed: button[tabindex]
```