sql_mode='ansi' is not resulting invalid use of group_by error

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
```sql
drop table if exists t1;
CREATE TABLE t1 (a int, b int);
INSERT INTO t1 VALUES (2,22),(1,11),(2,22);
SET @@sql_mode='ansi';
SELECT a FROM t1 WHERE (SELECT COUNT(b) FROM DUAL) > 0 GROUP BY a;
```

### 2. What did you expect to see? (Required)
```sql
mysql> SELECT a FROM t1 WHERE (SELECT COUNT(b) FROM DUAL) > 0 GROUP BY a;
ERROR 1111 (HY000): Invalid use of group function
```
### 3. What did you see instead (Required)
```sql
mysql> SELECT a FROM t1 WHERE (SELECT COUNT(b) FROM DUAL) > 0 GROUP BY a;
+------+
| a |
+------+
| 2 |
| 1 |
+------+
2 rows in set (0.00 sec)
```
### 4. What is your TiDB version? (Required)

```sql
mysql> select version();
+-----------------------------------------------+
| version() |
+-----------------------------------------------+
| 5.7.25-TiDB-v6.1.0-alpha-482-g81a852077-dirty |
+-----------------------------------------------+
```