cubicweb #3064075 [testlib] temporary_appobjects should call __registered__ if any [validation pending]

as this is done during regular registration.

prioritynormal
typebug
done in3.17.6
load0.100
load left0.000
closed by#0d346a0a1451 [testlib] temporary_appobjects should call __registered__ if it exists. Closes #3064075
patch[testlib] temporary_appobjects should call __registered__ if it exists. Closes #3064075 [applied]