TiDB sees both old and updated row in the single SELECT result

## Bug Report

I was playing with TiDB transactions and discovered an interesting artifact which I can’t explain. Basically in case of parallel updates the transaction was able to see both original row and the updated one together returned by a single SELECT statement.

### 1. Minimal reproduce step (Required)
Create table:
```
# primary key is important
create table t (i int primary key);
Insert into t values (0);
```

Start one transaction:
```
Txn_1:
BEGIN;
Select * from t;
+---+
| i |
+---+
| 0 |
+---+
```

Update in the separate transaction:
```
Txn_2:
begin;
update t set i = 1;
commit;
````

Update same table in the original transaction:
```
Txn_1:
Update t set i = 2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
```

### 2. What did you expect to see? (Required)
Original transaction should see only updated value:
```
Txn_1:
mysql> select * from t;
+---+
| i |
+---+
| 2 |
+---+
```
I actually observe this, but only after `commit` statement.

### 3. What did you see instead (Required)
Original transaction see both values:
```
mysql> Select * from t;
+---+
| i |
+---+
| 0 |
| 2 |
+---+
```

### 4. What is your TiDB version? (Required)

```
| Release Version: v7.6.0
Edition: Community
Git Commit Hash: 52794d985ba6325d75a714d4eaa0838d59425eb6
Git Branch: heads/refs/tags/v7.6.0
UTC Build Time: 2024-01-22 14:13:53
GoVersion: go1.21.5
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
```