docs(python): Update write_database code blocks in user guide

[JackRolfe]

Description

The current Python code block example in the user guide for writing to a database returns an error on the latest stable release. The specific issue is "uri=uri".

The py-polars polars.DataFrame.write_database API reference documentation uses the "connection" instead of "uri".

Links:

• https://docs.pola.rs/user-guide/io/database/#write-to-a-database
• https://docs.pola.rs/py-polars/html/reference/api/polars.DataFrame.write_database.html

Link

https://docs.pola.rs/user-guide/io/database/#write-to-a-database