start testing with python 3.13

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.56%. Comparing base (b18d8df) to head (5b18e13). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #159 +/- ## ======================================= Coverage 98.56% 98.56% ======================================= Files 18 18 Lines 2223 2223 Branches 230 230 ======================================= Hits 2191 2191 Misses 21 21 Partials 11 11 ``` | [Flag](https://app.codecov.io/gh/alexgolec/schwab-py/pull/159/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Golec) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/alexgolec/schwab-py/pull/159/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Golec) | `98.56% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alex+Golec#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.