resultRelInfo is the argument for the function, not projectReturning.
Author: Etsuro Fujita
Discussion: https://postgr.es/m/
5AA8E11E.
1040609@lab.ntt.co.jp
/*
* ExecProcessReturning --- evaluate a RETURNING list
*
- * projectReturning: RETURNING projection info for current result rel
+ * resultRelInfo: current result rel
* tupleSlot: slot holding tuple actually inserted/updated/deleted
* planSlot: slot holding tuple returned by top subplan node
*