Drop the temporary tuple slots allocated by pgoutput.

In pgoutput, when converting the child table's tuple format to match the
parent table's, we temporarily create a new slot to store the converted
tuple. However, we missed to drop such temporary slots, leading to
resource leakage.

Reported-by: Bowen Shi
Author: Hou Zhijie
Reviewed-by: Amit Kapila
Backpatch-through: 15
Discussion: https://postgr.es/m/CAM_vCudv8dc3sjWiPkXx5F2b27UV7_YRKRbtSCcE-pv=cVACGA@mail.gmail.com

Author: Amit Kapila

src/backend/replication/pgoutput/pgoutput.c

@@ -1554,6 +1554,16 @@ pgoutput_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 		ancestor = NULL;
 	}
 
+	/* Drop the new slots that were used to store the converted tuples. */
+	if (relentry->attrmap)
+	{
+		if (old_slot)
+			ExecDropSingleTupleTableSlot(old_slot);
+
+		if (new_slot)
+			ExecDropSingleTupleTableSlot(new_slot);
+	}
+
 	MemoryContextSwitchTo(old);
 	MemoryContextReset(data->context);
 }