[dataimport] prepare_insert_entity should not crash with SQLGenObjectStore
grafted from 1079d68130e1e780791ceb2050e8a8b7a910f48d (3.22)
related to #9177565.
usr/lib/python2*/*-packages/cubicweb/dataimport/
usr/lib/python2*/*-packages/cubicweb/server/
usr/lib/python2*/*-packages/cubicweb/hooks/
usr/lib/python2*/*-packages/cubicweb/sobjects/
usr/lib/python2*/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/