Refactor/simplify test matrix

[luke-hill]

🤔 What's changed?

Follow up from previous work in #586 to explain the decisions. Move to an include/exclude matrix to cover old/new rubies vs standard ones

⚡️ What's your motivation?

Explain the choices of what combinations to run plus simplify things a little (Removing some redundant combinations in the process).

🏷️ What kind of change is this?

• 📖 Documentation (improvements without changing code)
• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[luke-hill]

cc/ @p8 / @olleolleolle for some updates here (We actually reduce the size of the matrix, but build it in a slightly diff way so you can see "how" it is built better).

[luke-hill]

ping @p8 this is now merged in. I probably will update the changelog soon as this is a reasonably important change (As we're now 'officially' supporting rails 7.2 - I'll probably also cut a patch version just to signify this also.

[p8]

Thanks @luke-hill !