ci: start testing against Python 3.13

[alcarney]

Description (e.g. "Related to ...", etc.)

Python 3.13 will be coming soon.
Opening this PR to see what, if any impact 3.13 has on pygls.

We might also want to consider the free threaded version at some point?

Code review checklist (for code reviewer to complete)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Commit messages are meaningful (see this for details)
• Tests have been included and/or updated, as appropriate
• Docstrings have been included and/or updated, as appropriate
• Standalone docs have been updated accordingly

Automated linters

You can run the lints that are run on CI locally with:

poetry install --all-extras --with dev
poetry run poe lint

[alcarney]

@tombh I've now also dropped Python 3.8 from the CI matrix, it's a little early (3.8 goes end of life on Oct 31st) but since it's a breaking change I think it makes sense to do it now along with #487

If you're happy with that, it looks like we will need to also remove the 3.8 pipelines from the list of required CI jobs.

[tombh]

Sounds good.

So the idea is to publish this as a release candidate along with the breaking changes in #487. That way we're not forcing dropped Python 3.8 support in our official release.

Our own CI runs will stop testing against 3.8 but that doesn't really affect the public, it just raises a very minor risk of not catching any 3.8-only bugs in the next 2 months.

I'm on board: I've disable the CI requirement for Python 3.8 in the test matrix ✅

(I've also added a new requirement for Python 3.12 tests, which I should have added a while ago.)

[alcarney]

Sounds good, also gives people chance to try porting before we officially release v2