Test open-edx-proposals on Ubuntu 24.04

[feanil]

This repository is using Ubuntu 20.04 for testing. That version of Ubuntu will be out of support before Teak. Therefore this repo needs to be updated to testing with Ubuntu 24.04 before Sumac is cut to allow everyone sufficient time to switch to the new version.

Update this repository to test with Ubuntu 24.04 so that we can make the switch.

• [ ] Tests are run and passing on Ubuntu 20.04 and 24.04
• [ ] If major changes were needed and this is a library, a new version is published to PyPI or NPM

Note: In some cases, it may not make sense to test with both the old and the new version. For example, if the workflow is running linting or publishing to a package manager. In these cases, simply update the workflow to run on the newer version or opt to set it to ubuntu-latest instead if it doesn't matter what version it's running on. If you're unsure, reach out to the maintenance working group in #wg-maintenance in slack for guidance.

Known affected workflow files:

• .github/workflows/ci.yml

[sarina]

@feanil I just migrated ci to ubuntu-latest since this is just OEP repo, in #627. Is that sufficient or would you like me to run ci on both 20.04 and latest?

[robrap]

@sarina: I approved the PR. I think you are all set.