Drop support for Python 3.8

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).

openedx / edx-django-utils