Named Spack environments
For the moment it's fine to have a single spack env on the Mac CI runner, but I guess on a longer term it would make sense to have named environments, a bit like what we have for named docker files for linux images.
e.g.
$ spack env create km3net-2023-04-14 2023-04-14.yaml
...
$ spack env create km3net-2023-05-04 2023-05-04.yaml
...
$ spack env list
==> 2 environments
km3net-2023-04-14 km3net-2023-05-05
...
$ spack env activate km3net-2023-05-05