📝 Update code examples to Python 3.9

[YuriiMotov]

Note that target branch is drop-python3.8-support.

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There seems to be a mistake in cov_tmp_path fixture - it copied coverage file into wrong directory, so it wasn't reflected in coverage final report. I fixed it in this commit

[github-actions]

📝 Docs preview

Last commit eec65c6 at: https://05564b02.sqlmodel.pages.dev

Modified Pages

• https://05564b02.sqlmodel.pages.dev/management-tasks/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/automatic-id-none-refresh/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/code-structure/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/create-db-and-table/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/delete/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/fastapi/tests/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/insert/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/select/ - (before)
• https://05564b02.sqlmodel.pages.dev/tutorial/update/ - (before)

[tiangolo]

Awesome, thank you! 🙌 🚀