- Drop end-of-life'd rails versions: 5.2, 6.x, <7.2

- Drop end-of-life’d ruby versions 3.0, 3.1
- Test with current versions of Rails: 7.2, 8.0, and ruby >=3.2
- Fix warning: add observer as runtime dependency
- Mark 3 tests as pending to the open bug on deleted models
- Convert project to GitHub Actions

Release merit v4.0.0, update NEWS

[fixes #335]

Release merit v3.0.3, update NEWS

Removes Hound badge (I don't think it's still reviewing PRs here).

Release merit v3.0.1, update NEWS

[ci skip]

Release version 3.0.0

[fixes #274] [ci skip]

Release v2.4.0