Code macro scroll controls are not keyboard accessible

This is a violation of WCAG Success Criterion 2.1.1

This [fails the wcag build|https://ci.xwiki.org/job/XWiki%20Environment%20Tests/job/xwiki-platform/job/master/215/testReport/org.xwiki.export.pdf.test.ui/AllITs/MySQL_8__Tomcat_9_jdk11__Chrome___Docker_tests_for_xwiki_platform_export_pdf___Build_for_MySQL_8__Tomcat_9_jdk11__Chrome___Docker_tests_for_xwiki_platform_export_pdf______/]:

WCAG fails in the test class [org.xwiki.export.pdf.test.ui.AllITs]:
__________
Validation in the test method [codeMacro]
Check for [org.xwiki.test.ui.po.ViewPage] at http://xwikiweb:8080/xwiki/bin/view/PDFExportIT/CodeMacro.
Found [1] items

1: Scrollable region must have keyboard access
Description: Ensure elements that have scrollable content are accessible by keyboard
Help URL: https://dequeuniversity.com/rules/axe/4.6/scrollable-region-focusable?application=axeAPI
Help: Scrollable region must have keyboard access
Impact: moderate
Tags: cat.keyboard, wcag2a, wcag211

HTML element:
<div class="box"><div class="code">// This is a very long comment that gets cut when exported to PDF because it exceeds the print page width and the code macro preserves spaces which means it has to be displayed on a single line.</div></div>
Selector: [.box]
Fix any of the following:
Element should have focusable content
Element should be focusable

==> expected: <false> but was: <true>

Here is a screenshot in context of this violation:

Scroll overflow elements are supported by Firefox (the violation is not an issue there), but not on Chrome.

The element should be focusable  (tabindex=0) for the scroll to be operated. There is no need to add extra scrolling logic, since this part is the responsibility of the browser.