Tests failing on MacOS 14

[mattjbr123]

At the moment I cannot get the advanced unit tests to run on MacOS 14 (at the time of writing the MacOS version available under the macos-latest tag) because of issues with gfortran.
The command gfortran is not made available by default, as there are several different versions of gfortran that the user could want, and so there are instead aliases to gfortran that point to specific versions. This means these aliases need to be included specifically in code that runs on MacOS, which they are not in the UniFHy tests because the tests also need to run on Ubuntu (though I imagine this could be fixed with if statements or equivalent if I could be bothered).
To get around this the gfortran command is linked/aliased to the gfortran version wanted as a task that only runs for the tests that run on MacOS. This task no longer works for MacOS-14, maybe because the libraries are now accessible under a different path, or perhaps for some more complicated reason that I didn't have time to look into.
Therefore for now, the tests only run on MacOS-13 until such time can be found to figure it out. @ThibHlln might have some insight?