Relax required ruby version to support Ruby 4

[vlado]

What does this pull request do?

Ruby 4.0.0 was released in December, but elastic-apm currently caps required_ruby_version at < 4.0, so it can't be installed on Ruby 4.0 even though the agent is compatible. This PR lifts that cap and adds Ruby 4.0 to CI.

Why is it important?

Checklist

• I have signed the Contributor License Agreement.
• My code follows the style guidelines of this project (See .rubocop.yml)
• I have rebased my changes on top of the latest main branch
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have made corresponding changes to the documentation
• I have updated docs/release-notes/index.md
• I have updated docs/reference/supported-technologies.md
• Added an API method or config option? Document in which version this will be introduced

[smith]

@vlado thanks for adding this! Sorry for the delayed response. Looks like there are some CI failures related to gem versioning. I haven't looked into it yet but you should be able to look the action run to see what when wrong: https://github.com/elastic/apm-agent-ruby/actions/runs/28862730853/job/89545484006?pr=1650

[vlado]

Thanks @smith

I've fixed the exclusion config but looks like CI will not start without approval.

[smith]

@vlado looks like a couple of the 4.0 ones failed: one because of SQLite and one missing benchmark?

[vlado]

@smith For Rails 4 and 5 sqlite3 gem is pinned to version that can not be installed for Ruby 4. benchmark was un-defaulted in Ruby 4.0. Rails 6.1's require "benchmark" without declaring it in its gemspec. Since both 5.2 and 6.1 are EOL and do not claim compatibility with Ruby 4 I think we can safely exclude them from the matrix.

[smith]

I think we can safely exclude them from the matrix.

@vlado Sounds good to me. If you push that change I can re-run and we should be good to merge.

[vlado]

I think we can safely exclude them from the matrix.

@vlado Sounds good to me. If you push that change I can re-run and we should be good to merge.

@smith Change is pushed b78768f

Failing spec seems unrelated to my changes (Seems like Docker Hub outage)