Run-time linker error on ARM-based Mac

[duncanpo]

A number of issues on ARM-based Mac:

1. When building on it, build will be successful. Using it will return an "invalid Mex file" error where it fails to find libMatlabEngine.dylib.
2. The .mltbx file has no support for ARM-based Mac. Will complain about not finding the mex file, which is only available in .mexmaci64 but not .mexmaca64.
3. GitHub workflows has to be pinned to macos-12 instead of the latest macos-14 because macos-14 (also macos-latest) is ARM-based.

[duncanpo]

Fix is in main branch