chore: drop python3.9 support

[germa89]

Description

Dropping python3.9 official support.

Using python3.11 for official testing.

~~However, I am going to keep one outdated version (python3.9) as part of the CICD, just testing installation and imports.~~ Nevermind, to do this I need to install the library with --ignore-requires-python argument but since we are using an ansys/action probably it is not worthy to remove completely the action just for this smoke test.

Issue linked

NA

Checklist

• [ ] I have visited and read Develop PyMAPDL.
• [ ] I have tested my changes locally
• [ ] I have added necessary documentation or updated existing documentation.
• [ ] I have followed the PyMAPDL coding style guidelines.
• [ ] I have added appropriate unit tests that also ensure the minimal coverage criteria.
• [ ] I have reviewed my changes before submitting this pull request.
• [ ] I have linked the issue or issues that are solved to the PR if any.
• [ ] I have assigned this PR to myself.
• [x] I have marked this PR as draft if it is not ready to be reviewed yet.
• [x] I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)