cubicweb #2755994 .related: ensure the entities=False is actually honored [done]

Not the case since in cw_set_relation_cache we blindly fetch rset.entities(...).

prioritynormal
typebug
done in3.16.1
load0.200
load left0.000
closed by#5567a5117aeb [entity] ensure the .related(entities=False) parameter is honored all the way down (closes #2755994)
patch[entity] ensure the .related(entities=False) parameter is honored all the way down (closes #2755994) [applied]