ci_scripts: add check_versions.py

Migrate the check_versions.py script from wheel_builder. Much of the
script has been refactored with the following goals:

1. Use GitHub conventions (instead of GitLab)
2. Create GitHub-specific replacement functions where necessary
3. Simplify other functions where possible
4. Use more Pythonic styling
5. Remove comments where the code is self-documenting

More specifically:

- Replace usage of `glab` with the corresponding `gh` CLI
- Create a REPO variable pointing to "riseproject-dev/python-wheels",
  and use it wherever the wheel_builder was referenced (in calls to
  `glab`)
- Change configure_git_identity() to use a "github-actions[bot]" user
  and corresponding noreply email
- Change generated branch names' prefix from "gitlab-ci" to
  "github-actions"
- Remove some auth/login-related logic using tokens to generate
  automated PRs, since the GitHub project allows us to enable this in
  the repository settings (not programatically)
- Add dispatch_workflow() and create_upgrade_pr() functions for
  triggering a desired workflow (e.g. for a "matplotlib" upgrade, the
  script should trigger the "build-matplotlib.yml" and
  "test-matplotlib.yml" workflows for the target version(s) if the
  workflow scripts exist, or indicate otherwise if not possible
- Allow updating of default versions in workflow scripts when
  auto-generating upgrade PRs.
- Add "Trigger" labels to auto-generated PRs for the new versions
  detected.
- Importantly, limit the maximum number of versions to be targeted by an
  auto-generated PR to three, so as not to create a runaway build queue.
- Remove most comments, since the code objectives are obvious after the
  refactor

AI-Generated: Uses Claude Code Opus 4.7

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc