Fix and Re-Enable Ruby Testing on macos-latest

To unblock an upcoming release, PR https://github.com/KhronosGroup/OpenCL-SDK/pull/103 changed the GitHub runner for Ruby testing from macos-latest back to macos-13. This issue is to track fixing the CI config for Ruby on macos-latest and re-enabling testing with the latest runner.

For reference, the failure was:

```
Run rake test
rake test
shell: /bin/bash -e {0}
Warning OpenCL 1.2 loader detected!
Warning: could not find extension function clReleaseDeviceEXT!
Warning: could not find extension function clRetainDeviceEXT!
Warning: could not find extension function clCreateSubDevicesEXT!
Warning: could not find extension function clGetKernelSubGroupInfoKHR!
Warning: could not find extension function clGetGLContextInfoKHR!
/Users/runner/.local/share/gem/ruby/[3](https://github.com/KhronosGroup/OpenCL-SDK/actions/runs/8885606590/job/24397324466#step:6:3).0.0/gems/opencl_ruby_ffi-1.3.13/lib/opencl_ruby_ffi/opencl_ruby_ffi_base.rb:[4](https://github.com/KhronosGroup/OpenCL-SDK/actions/runs/8885606590/job/24397324466#step:6:5)45:in `error_check': -30 (OpenCL::Error::INVALID_VALUE)
from /Users/runner/.local/share/gem/ruby/3.0.0/gems/opencl_ruby_ffi-1.3.13/lib/opencl_ruby_ffi/Platform.rb:116:in `devices'
from /Users/runner/work/OpenCL-SDK/OpenCL-SDK/ruby/copybuffer/copybuffer.rb:19:in `'
from :136:in `require'
from :136:in `require'
from /opt/homebrew/Cellar/ruby@3.0/3.0.6_1/lib/ruby/gems/3.0.0/gems/rake-13.0.3/lib/rake/rake_test_loader.rb:17:in `block in '
from /opt/homebrew/Cellar/ruby@3.0/3.0.6_1/lib/ruby/gems/3.0.0/gems/rake-13.0.3/lib/rake/rake_test_loader.rb:[5](https://github.com/KhronosGroup/OpenCL-SDK/actions/runs/8885606590/job/24397324466#step:6:6):in `select'
from /opt/homebrew/Cellar/ruby@3.0/3.0.6_1/lib/ruby/gems/3.0.0/gems/rake-13.0.3/lib/rake/rake_test_loader.rb:5:in `'
rake aborted!
Command failed with status (1)

Tasks: TOP => test
(See full trace by running task with --trace)
```

Start with PR #103 and the GitHub Actions Ruby testing configuration changed there. Reproduce the macos-latest failure by running the Ruby test workflow, then trace the failure through ruby/copybuffer/copybuffer.rb and the reported opencl_ruby_ffi device lookup. Done means Ruby testing is re-enabled on macos-latest and the rake test step passes.

Written by the indexing model from the issue text.