CI (Git) Update, master branch (2022.04.05.)
Made the CentOS 7 builds pick up git from CVMFS. This is needed to make CMake 3.21.3 capable to downloading the latest version of GeoModel. CC7's old git version is what made !935 (closed) fail so far.
At the same time removed all remnants of the CentOS 8 build setup, and defined the versions of CMake and Git to use in the CI in one central place. (So that it would be easier to upgrade them later on.)