Update classifier to support Python 3.13

[shenxianpeng]

Based on CI, pip should already support Python 3.13, so the classifier should also have Python 3.13 included.

https://github.com/pypa/pip/blob/a7369ba1452b93dc70cb2f5c21c1ffa249202ec8/.github/workflows/ci.yml#L117

[webknjaz]

Based on CI, pip should already support Python 3.13, so the classifier should also have Python 3.13 included.

Technically, until Python 3.13 hasn't hit the final release stage itself, it could still break things. But of course, it's up to the pip maintainers who might follow different principles than I do :man_shrugging:

[shenxianpeng]

Python 3.13 was officially released on October 7, 2024. Ready for merging?

[webknjaz]

@pradyunsg easy merge?