chore: removing ruby-head from CI

[tiwarishubham635]

Fixes

Failing job - https://github.com/twilio/twilio-ruby/actions/runs/14993570192/job/42122563880

ruby-head on CI is built from the latest commit(s) on Ruby’s master branch - https://github.com/ruby/ruby
It seems that there might be some unstable changes in the branch which leads to test failure. Removing the version for now, to pass the tests

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud