cubicweb #5705769 removal of InternalManager._cw breaks stuff [validation pending]

entity.py tries to get at user._cw.vreg, which now raises AttributeError

prioritynormal
typebug
done in3.21.1
load0.250
load left0.000
closed by#08c5d26417f6 [server] stick a _cw on internal connnection's user
patch[server] stick a _cw on internal connnection's user [applied]