cubicweb #1776091 UndoController output is broken [resolved]

a raw string is returned directly by the controller whci breaks output when we have unicode in cubicweb.etwist.http._finalize().

prioritynormal
typebug
done in3.12.10
load0.500
load left0.000
closed by#a397305f3976 [controller] UndoController: fix output method (closes: #1776091)