cubicweb-worker #3892249 [migration] fix it all [resolved]

Wasn't tested, was broken.

prioritynormal
typebug
done in3.0.1
load0.200
load left0.000
closed by#54b315c3a6c7 [migration] fix migration to 3.0.0 (closes #3892249)
patch[migration] fix migration to 3.0.0 (closes #3892249) [applied]