mysql: `DROP INDEX idx_xxx on t` and an error occurs

With v0.56.0 using the mysql dialect, use the `parse_sql` function to parse `DROP INDEX idx_name ON table_demo;` or `ALTER TABLE tbl_name DROP INDEX idx_name;` and an error occurs.

```rust
use sqlparser::dialect::MySqlDialect;
use sqlparser::parser::Parser;

fn main() {
let sql = "DROP INDEX idx_name ON table_demo;";

let dialect = MySqlDialect {}; // or AnsiDialect, or your own dialect ...

let ast = Parser::parse_sql(&dialect, sql).unwrap();

println!("AST: {:?}", ast);
}

```

Report the following error:

```
called `Result::unwrap()` on an `Err` value: ParserError("Expected: end of statement, found: ON at Line: 1, Column: 21")
```

In the official documentation of MySQL, when deleting an index, you need to specify the table where the index is located.

```sql
DROP INDEX index_name ON tbl_name
[algorithm_option | lock_option] ...

algorithm_option:
ALGORITHM [=] {DEFAULT | INPLACE | COPY}

lock_option:
LOCK [=] {DEFAULT | NONE | SHARED | EXCLUSIVE}

```

https://dev.mysql.com/doc/refman/8.0/en/drop-index.html

Would you classify this as a bug?

Riproducete il problema tramite MySqlDialect e Parser::parse_sql utilizzando sia la forma DROP INDEX ... ON ... sia la forma ALTER TABLE ... DROP INDEX. Tracciate il modo in cui queste istruzioni vengono analizzate e verificate che la copertura di regressione accetti la sintassi MySQL documentata senza l’errore del parser segnalato.

Scritto dal modello di indicizzazione a partire dal testo della issue.