wrong results when the query contains setting user var

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
create table t(a int, b int, index idx_a(a));
insert into t values (1,2), (3,4);
-- repeat the following insert for 16 times
insert into t select a + 1, b + 1 from t;
insert into t select a + 1, b + 1 from t;
...
insert into t select a + 1, b + 1 from t;

SELECT i, a AS aa FROM
(
SELECT
(@i := @i + 1) AS i,
t1.a
FROM
(SELECT a FROM t ORDER BY a) t1,
(SELECT @i := 0) AS x
ORDER BY
a
) tmp limit 10;
```

### 2. What did you expect to see? (Required)
MySQL's results:
```
mysql> SELECT i, a AS aa FROM
-> (
-> SELECT
-> (@i := @i + 1) AS i,
-> t1.a
-> FROM
-> (SELECT a FROM t ORDER BY a) t1,
-> (SELECT @i := 0) AS x
-> ORDER BY
-> a
-> ) tmp limit 10;
+------+------+
| i | aa |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 2 |
| 4 | 2 |
| 5 | 2 |
| 6 | 2 |
| 7 | 2 |
| 8 | 2 |
| 9 | 2 |
| 10 | 2 |
+------+------+
10 rows in set, 2 warnings (0.11 sec)
```

### 3. What did you see instead (Required)
TiDB's results:
```
mysql> SELECT i, a AS aa FROM
-> (
-> SELECT
-> (@i := @i + 1) AS i,
-> t1.a
-> FROM
-> (SELECT a FROM t ORDER BY a) t1,
-> (SELECT @i := 0) AS x
-> ORDER BY
-> a
-> ) tmp limit 10;
+------+------+
| i | aa |
+------+------+
| 1025 | 1 |
| 1034 | 2 |
| 1030 | 2 |
| 1033 | 2 |
| 1027 | 2 |
| 1029 | 2 |
| 1031 | 2 |
| 1032 | 2 |
| 1026 | 2 |
| 1028 | 2 |
+------+------+
10 rows in set (0.55 sec)
```
Looking into the execution plan, No order is guaranteed when pulling data from `HashJoin_25`, which doesn't match the meaning of the query.
```
mysql> explain SELECT i, a AS aa FROM
-> (
-> SELECT
-> (@i := @i + 1) AS i,
-> t1.a
-> FROM
-> (SELECT a FROM t ORDER BY a) t1,
-> (SELECT @i := 0) AS x
-> ORDER BY
-> a
-> ) tmp limit 10;
+---------------------------------+-----------+-----------+-------------------------+---------------------------------------------------+
| id | estRows | task | access object | operator info |
+---------------------------------+-----------+-----------+-------------------------+---------------------------------------------------+
| TopN_17 | 10.00 | root | | test.t.a, offset:0, count:10 |
| └─Projection_22 | 131072.00 | root | | setvar(i, plus(getvar(i), 1))->Column#5, test.t.a |
| └─HashJoin_25 | 131072.00 | root | | CARTESIAN inner join |
| ├─Projection_26(Build) | 1.00 | root | | setvar(i, 0)->Column#4 |
| │ └─TableDual_27 | 1.00 | root | | rows:1 |
| └─IndexReader_35(Probe) | 131072.00 | root | | index:IndexFullScan_34 |
| └─IndexFullScan_34 | 131072.00 | cop[tikv] | table:t, index:idx_a(a) | keep order:true |
+---------------------------------+-----------+-----------+-------------------------+---------------------------------------------------+
7 rows in set (0.00 sec)
```

### 4. What is your TiDB version? (Required)
```
mysql> SELECT tidb_version();
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version() |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v5.4.0-1263-gc7b5ca0f7
Edition: Community
Git Commit Hash: c7b5ca0f716f373a2d79760817e1069c196b290c
Git Branch: master
UTC Build Time: 2022-08-06 05:32:04
GoVersion: go1.18.1
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: unistore |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```