RealtimeWYSIWYGEditorIT#dragAndDropFilesAtTheSameTime is flickering

org.opentest4j.AssertionFailedError: 
expected: <first [[attach:realtimeWysiwygEditor.webm||target="_blank"]] red [[image:ckeditor-source.png]] yellow end

second [[attach:source-button.mp4||target="_blank"]] blue [[image:realtimeWysiwygEditor.png]] green> but was: <f

second [[attach:source-button.mp4||target="_blank"]] b yellow lue [[image:realtimeWysiwygEditor.png]] green>
	at org.xwiki.realtime.wysiwyg.test.ui.RealtimeWYSIWYGEditorIT.dragAndDropFilesAtTheSameTime(RealtimeWYSIWYGEditorIT.java:1818)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)