[GH] Automation should use `cccl-version.json@main` as current release source-of-truth

`project_automation_set_roadmap.yml` moves all issues to the first roadmap entry when they're closed, and assumes that the first release listed is always the current one.

This forces the roadmap values into an awkward order, and prevents sorting issues accurately by milestone.

This issue can be closed when the project automation is updated to query the `cccl-version.json` file on `main` as the source of truth for newly merged PRs. Ideally this would be done by fetching the file with wget / curl rather than cloning the full repo.

Open project_automation_set_roadmap.yml and trace how newly merged PRs determine their roadmap entry. Read the cccl-version.json file on main and test fetching it with wget or curl instead of cloning the repository. Done means newly merged PRs use the current release from that file rather than assuming the first roadmap entry.

Written by the indexing model from the issue text.