Drop support for Python 3.8

[irtazaakram]

Description:

Follow and complete all of the following steps for the issue to be marked as done.

• [ ] Update the tox.ini, setup.py, setup.cfg, or pyproject.toml to remove Python 3.8 from the supported versions list.
• [ ] Ensure the GitHub Actions workflows are updated, particularly removing Python 3.8 from the CI matrix.
• [ ] Review and clean up any testing or build configurations referencing Python versions earlier than 3.11.
• [ ] Run tests in the CI to ensure everything passes after removing Python 3.8.
• [ ] Add a CHANGELOG entry: “Dropped support for Python 3.8.”
• [ ] Bump the package version and release a new version on GitHub & PyPI (if applicable).

[iamsobanjaved]

PR to drop support for Python 3.8

• https://github.com/openedx/auth-backends/pull/333

@huniafatima-arbi kindly complete if any item is pending from the checklist otherwise close the issue.