Also test older cmake versions (#7347)

Also test older cmake versions (#7347)

This PR generally improves the new CI job to test different cmake versions. It extends the tested versions back to 3.8 and also sets the minimum required version (cmake_minimum_required) to the version that is tested. This allows to check compatibility with changing cmake policies.
It also modifies the run-tests action to get the regression options from explicit inputs instead of the build matrix. As the cmake job had no build matrix, it used to build regress3-4 as well.