Fix unit test failures on recent macOS ARM platforms

As discussed [on Slack](https://opencolorio.slack.com/archives/C3Q43TN4Q/p1706842156429159), several people have reported that the CPU and GPU unit tests fail on macOS ARM chips with macOS 14.

Our experiments to set up a macOS ARM CI runner (also macOS 14) [ran into similar problems.](https://github.com/AcademySoftwareFoundation/OpenColorIO/actions/runs/7677346079)

It looks like many of the failures are probably ok but just slightly outside the existing tolerances or are happening where there currently are no tolerances in the test but should be.

This task will require going through the failing tests one by one and deciding what to do. If you want to take this on, please reach out on Slack and run into questions about a given test.