Added support for Rails 8

[basex]

Followed the same as #752

I tested locally and works without issues.

In the future if we stop supporting Rails 2 we can check for Rails::VERSION::MAJOR. Example: Rails::VERSION::MAJOR > 6

[tagliala]

Hi, thanks for this PR.

Failures do not depend by this PR. I have some small changes to do to the CI, then I'll ask to rebase

[tagliala]

@basex please rebase, specs should pass

[basex]

done @tagliala Thanks

[tagliala]

All green, let me try if I remember how to run integration tests. Did you run it locally?

[tagliala]

Sorry, rabl needs some other changes that are not related to this PR.

I will make the changes elsewhere and then ask to rebase or cherry-pick your commit to preserve your authoring

[tagliala]

Thanks,

I've performed an integration test locally against rails 8 and it worked, however we now have two options

1. I'll cherry-pick this commit in a new PR and make the change. You will be preserved as an author of the commit, but I'm not sure that your name will appear in the automatic release notes
2. You create a new branch on your fork, possibly with a good name, let's say rails8, then:

• Cherry pick basex/rabl@1c45233 on that branch
• Reset your fork master branch on this gem's master
• Rebase rails8 on master, submit a new PR

Point 2 would also apply as best practice for future PRs. It is required to have a single clean commit to merge here (I do not have the "rebase" feature available, maybe because it's the master branch on the remote fork)

Please also add the following at the top of CHANGELOG.md

## unreleased

* Add Rails 8 compatibility (@basex)

[basex]

Discarding the commits in my fork automatically closed this MR. New PR from another branch here #768