SQLModelGenerator does not respect table names

Love the addition of the SQLModelGenerator. However the generated models transform the table names in undesired ways (e.g. `some_random_table` becomes `somerandomtable`).

Removing `render_class_variables` from the SQLModelGenerator class, or simply calling `super().render_class_variables` there fixes the issue. `DeclarativeGenerator.render_class_variables` adds the `__tablename__` class variable, which is supported by SQLModel, see [here](https://github.com/tiangolo/sqlmodel/issues/159#issuecomment-978357069).

I'm happy to open a PR, but I'm not sure if this would have unintended consequences (or if there's a better way to accomplish this).