Set operations might skip the earlier tenant accesses on citus_stat_tenants

```SQL

SELECT citus_stat_tenants_reset();

(SELECT * FROM simple_test WHERE a = 1 ) UNION (SELECT * FROM simple_test WHERE a = 2) UNION (SELECT * FROM simple_test WHERE a = 3);

select nodeid,colocation_id,tenant_attribute,query_count_in_this_period from citus_stat_tenants;
nodeid | colocation_id | tenant_attribute | query_count_in_this_period
--------+---------------+------------------+----------------------------
2 | 1 | 2 | 1
2 | 1 | 3 | 1
(2 rows)

```

I think we should either have all or none. In general, we seem to have `none` when more than 1 shard involved, which makes sense