preparing a query that causes warning should not create warning until executing it

In addition to https://github.com/dolthub/dolt/issues/6921, running a query that causes warnings as prepared doubles the warnings.

Dolt:
```
mysql> prepare d from "drop table if exists table1, table2, table3;";
Query OK, 0 rows affected, 6 warnings (0.00 sec)
Statement prepared

mysql> show warnings;
+-------+------+------------------------+
| Level | Code | Message |
+-------+------+------------------------+
| Note | 1051 | Unknown table 'table3' |
| Note | 1051 | Unknown table 'table2' |
| Note | 1051 | Unknown table 'table1' |
| Note | 1051 | Unknown table 'table3' |
| Note | 1051 | Unknown table 'table2' |
| Note | 1051 | Unknown table 'table1' |
+-------+------+------------------------+
6 rows in set, 6 warnings (0.00 sec)

mysql> execute d;
Query OK, 0 rows affected, 9 warnings (0.00 sec)

mysql> show warnings;
+-------+------+------------------------+
| Level | Code | Message |
+-------+------+------------------------+
| Note | 1051 | Unknown table 'table3' |
| Note | 1051 | Unknown table 'table2' |
| Note | 1051 | Unknown table 'table1' |
| Note | 1051 | Unknown table 'table3' |
| Note | 1051 | Unknown table 'table2' |
| Note | 1051 | Unknown table 'table1' |
| Note | 1051 | Unknown table 'table3' |
| Note | 1051 | Unknown table 'table2' |
| Note | 1051 | Unknown table 'table1' |
+-------+------+------------------------+
9 rows in set, 9 warnings (0.00 sec)
```

MySQL:
```
mysql> prepare d from "drop table if exists table1, table2, table3;";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> show warnings;
Empty set (0.00 sec)

mysql> execute d;
Query OK, 0 rows affected, 3 warnings (0.00 sec)

mysql> show warnings;
+-------+------+-----------------------------+
| Level | Code | Message |
+-------+------+-----------------------------+
| Note | 1051 | Unknown table 'mydb.table1' |
| Note | 1051 | Unknown table 'mydb.table2' |
| Note | 1051 | Unknown table 'mydb.table3' |
+-------+------+-----------------------------+
3 rows in set (0.00 sec)

```