cubicweb-tracker #9765833 modification_date should be set with a tz [validation pending]

otherwise things break with cubicweb 3.22 (e,g. the edit controller gets very sad if entities have a modification date in the future)

priorityimportant
typebug
done in1.17.2
load1.000
load left0.000
closed by#14b5265b1af4 [hooks] compatibility with cubicweb 3.22