R tests on Github fail with macos-latest runner

[saikonen]

#1814 swapped R test runner to ubuntu, due to them failing with macos-latest runners since the macos 14 update.

Suggest looking into eventually fixing R tests so they can be run on macos-latest, as this should be a more common platform among users requiring the R support.

[ayushranjan2]

Key areas to investigate:

• R package installation issues on macos 14
• Test environment differences between macos and Ubuntu
• Potential platform-specific test assumptions