[predicates] keep making `yes` predicate importable from cubicweb (closes #2790319) The `yes` predicate was moved out in CubicWeb 3.15 but it should have remained importable from the cubicweb.predicates module, for bw compat reasons and also because logilab.common.registry is an implementation detail.

change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')