Add testing against Python 3.13

[chosak]

This PR adds testing against Python 3.13.

Notes and todos

Currently these changes replace the version of Python tested in tox.ini (and GitHub Actions) with Python 3.13 instead of Python 3.8. Before this PR is merged, this needs to be changed to test these simultaneously (if we want to support both versions at the same time). This PR currently only demonstrates the necessary changes for tests to pass against 3.13.

This PR includes changes from #8715 which pass unnoticed in 3.8 but cause actual test failures against 3.13.

This PR does not alter site documentation nor any of the cf.gov Dockerfile implementations.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code follows the standards laid out in the CFPB development guidelines
• Future todos are captured in comments and/or tickets
• Project documentation has been updated, potentially one or more of:
  • This repo’s docs (edit the files in the /docs folder) – for basic, close-to-the-code docs on working with this repo
  • CFGOV/platform wiki on GHE – for internal CFPB developer guidance
  • CFPB/hubcap wiki on GHE – for internal CFPB design and content guidance

Front-end testing

Browser testing

Check the current browser support cutoff list](https://cfpb.github.io/consumerfinance.gov/browser-support#current-browser-support-metrics) for browsers that are advisable
to prioritize for testing.

Accessibility

• Keyboard friendly (navigable with tab, space, enter, arrow keys, etc.)
• Screen reader friendly
• Does not introduce new errors or warnings in WAVE

Other

• Is useable without CSS
• Is useable without JS
• Does not introduce new lint warnings
• Flexible from small to large screens