Updating repositories when they exist already

Discussion with Ashwin

• spack environments repositories should be updated if they exist:
  • released versions (correesponding to released branches) such as dev-23a, should not change anyway
  • for development versions we want the latest version

Same argument applies for for our mpsd-spack clone (already done in https://gitlab.gwdg.de/mpsd-cs/spack-environments/-/blob/develop/spack_setup.sh#L97).