Fix the configuration of Mac CI-machines

The configuration of the Mac CI-machines were corrupted after some upgrade or installation of new packages. More precisely, brew-generated symlinks were incorrect.

Seemingly, brew produces/updates the symlinks after installation of new packages or upgrades. For our build system, where we need multiple versions of Python and Qt, this can lead to a state where cmake find-package mechanism is confounded; sometimes even after finding the right packages, errors appear late, during the build phase.

I upgraded the packages on Mac 10.15 and 12.10, and corrected the paths in GitLab-CI YAML file.