feat: drop support for python 3.9

[afuetterer]

What does this PR do?

This PR removes support for Python 3.9 which reaches EOL in 10/2025.

See https://devguide.python.org/versions.

Before submitting

• This PR fixes a typo or improves the docs (if yes, ignore all other checks!).
• Did you read the contributor guideline?
• Was this discussed/approved via a Github issue? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes (if applicable)?
• Did you write any new necessary tests?

[MaartenGr]

Thank you for your active work on this; it is greatly appreciated!