Fix compiler error introduced by 5386bfb9c1.

Per buildfarm member wrasse, void function cannot return a value.
This only affects v13-v17, where an ABI-compatible wrapper function
was added.

Backpatch-through: 13-17

src/backend/executor/execMain.c

@@ -1148,8 +1148,8 @@ void
 CheckValidResultRel(ResultRelInfo *resultRelInfo, CmdType operation,
 					List *mergeActions)
 {
-	return CheckValidResultRelNew(resultRelInfo, operation, ONCONFLICT_NONE,
+	CheckValidResultRelNew(resultRelInfo, operation, ONCONFLICT_NONE,
-								  mergeActions);
+						   mergeActions);
 }
 
 /*