🐛 Fix `tuple_` return type annotation

[kakeruzoku]

Fixed an issue where sqlmodel.tuple_ returns <class 'sqlalchemy.sql.elements.Tuple'> but the type hint points to <class 'tuple'>.

The current workaround for this mistake, # type: ignore[return-value], has been removed.

https://github.com/fastapi/sqlmodel/blob/5c1b89afd9205884c46ff71819b327b00d185a3a/sqlmodel/sql/expression.py#L195