Query in transaction behavior is inconsistent with MySQL

## Bug Report

Please answer these questions before submitting your issue. Thanks!

This is a sub-issue of https://github.com/pingcap/tidb/issues/24195#issuecomment-906882492

### 1. Minimal reproduce step (Required)

```sql
/* t1 */ drop table if exists t;
/* t1 */ create table t (c1 varchar(10), c2 int, primary key(c1));
/* t1 */ insert into t values ('a', 1);
/* t1 */ begin;
/* t1 */ update t set c1='b' where c1='a';
/* t2 */ begin;
/* t2 */ insert into t values ('a', 2);
/* t1 */ commit;
/* t2 */ select * from t;
```

For the last query, TiDB return:

```sql
+----+----+
| c1 | c2 |
+----+----+
| a | 2 |
+----+----+
```

But MySQL 8.0.29 return:

```sql
+----+----+
| c1 | c2 |
+----+----+
| a | 2 |
| b | 1 |
+----+----+
```

Theoretically, transaction `t2` start_ts is small than transaction `t1`, then the last query shouldn't see row `b 1`.

But if transaction `t2` query once after begin, MySQL query result will same with TiDB:

```sql
/* t1 */ drop table if exists t;
/* t1 */ create table t (c1 varchar(10), c2 int, primary key(c1));
/* t1 */ insert into t values ('a', 1);
/* t1 */ begin;
/* t1 */ update t set c1='b' where c1='a';
/* t2 */ begin;
/* t2 */ select * from t;
/* t2 */ insert into t values ('a', 2);
/* t1 */ commit;
/* t2 */ select * from t;
```

For the last query, both TiDB and MySQL 8.0.29 return:

```
+----+----+
| c1 | c2 |
+----+----+
| a | 2 |
+----+----+
```

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

```sql
***************************[ 1. row ]***************************
tidb_version() | Release Version: v7.2.0-alpha-306-gc4756df3b4
Edition: Community
Git Commit Hash: c4756df3b4e6ba6b5a532e0999ac3a28c40fa31a
Git Branch: master
UTC Build Time: 2023-05-31 09:14:58
GoVersion: go1.20.2
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: unistore
```