Add support for Django 4.2 in enterprise-subsidy

[iamsobanjaved]

In order to have support for Django 4.2, we first need to run tests on Django 4.2 in the entrerprise-subsidy service. For updating CI, we should run tox and GitHub actions modernizers.

Tox Modernizer: tox_moderniser_django42.py

Github Action Modernizer: github_actions_modernizer_django42.py

A/C

Beta Give feedback

1. Fix Django 4.0 and 4.1 removal warnings
2. Run tests with Django 4.2
3. Fix all test failures with Django 4.2 (if any)
4. After merging, ask the owning squad to add Django 4.2 tests in branch protection rules

After completion kindly unblock this: https://github.com/orgs/edx/projects/12/views/8?pane=issue&itemId=39872878