Steps to reproduce the issue

Have 2 different editors on the page. Using this code I'm showing 'Editor - None' and 'Editor - CodeMirror' on the same page:

foreach (array('none', 'codemirror') as $plugin)
{
	$editor = \Joomla\CMS\Editor\Editor::getInstance($plugin);

	echo $editor->display($plugin, $plugin, 500, 320, 70, 10, true);
}

Expected result

Two editors with the same amount of buttons

Actual result

Buttons are duplicated on the second editor

Additional comments

Seems to be caused by these lines:
https://github.com/joomla/joomla-cms/blob/4.2-dev/libraries/src/Editor/Editor.php#L93-L104

Every time an editor is initialized the event listener is added. Might be an oversight because you won't notice this out of the box (I haven't found any page where the Joomla! CMS would present different editors).