Drop Python 3.9 support

[frenck]

Breaking change

Python 3.9 support has previously been deprecated and has now been removed. Home Assistant now requires Python 3.10 to run.

If you are using Home Assistant OS, Home Assistant Container, or Home Assistant Supervised installation method, you don't have to do anything. In those cases, we all handle this for you. Your system has been using Python 3.10 for quite some time already.

Proposed change

Drops support for Python 3.9, which was deprecated in #82193

Getting close to the beta cut for 2023.2.0, it becomes time to drop it from dev. I've just shipped the Home Assistant Core 2023.1.7 patch release, which we are now assuming will be the last patch release of 2023.1.x.

This PR focuses on dropping Python support in a minimal way. Additional refactoring has been left out of scope. It removes CI for Python 3.9, and enforces Python 3.10.

Additionally, there is a change in hassfest, since stdlib-list has been unmaintained and is no longer compatible. However, Python 3.10 now has a built-in replacement. The downside to this replacement is that it only supports the Python version it is run against. Yet, this is better than dropping it completely IMHO.

Nb: Refactoring and cleanups are left out of scope for this PR; as those should be done independently in separate PRs.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[frenck]

Alright, Home Assistant 2023.1.7 has been shipped (aimed to be the last patch release), and the next beta is just a couple of days away.

Ready for review & merge.

../Frenck

[frenck]

Thanks! 👍