Steps to reproduce the issue

Publish a menu module with layout default to the topbar position of the Cassiopeia template. Login to the Joomla frontend. Check the markup of the module in the frontend.

Expected result

Valid markup.

Actual result

<ul class="mod-menu mod-list nav foo-bar">
    <a class="btn btn-link jmodedit" href="#" target="_self" aria-describedby="tip-123">
    <span class="icon-edit" aria-hidden="true"></span><span class="visually-hidden">Edit</span></a>
    <div role="tooltip" id="tip-123">Edit Module<br>Test Menu<br>Position: below-top</div>
    <li class="nav-item item-101 default current active"></li>
</ul>

System information (as much as possible)

Joomla 4.0.*

Additional comments

The following line https://github.com/joomla/joomla-cms/blame/4.0-dev/layouts/joomla/edit/frontediting_modules.php#L40 will create invalid markup, if the module's outer tag is an <ul> or <ol>. (e.g.

The Unordered List element <ul may only contain <li>, <template>, <script> child elements.

Introduced with 678e929