Keep GitHub Actions up to date with Dependabot

[cclauss]

Resolves warnings on GitHub Actions runs like at the bottom of:
https://github.com/django-oscar/django-oscar/actions/runs/7585638224

https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot

https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#package-ecosystem

[codecov]

Codecov Report

Merging #4230 (2c63014) into master (8f57e5c) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4230   +/-   ##
=======================================
  Coverage   87.84%   87.84%           
=======================================
  Files         291      291           
  Lines       16145    16145           
=======================================
  Hits        14182    14182           
  Misses       1963     1963           

[cclauss]

@samar-hassan @specialunderwear Your reviews, please. In #4213 we can see that many GitHub Actions are out of date. It would be useful to bring them up to date before landing other pull requests.

• DRAFT: GitHub Actions: Test on Python v3.12 and Django v5.0 #4213