Do not show nix config in CI

Dependencies

• [2] AG72J7RH Add .gitlab-ci.yml
• [3] AQ3VVSXY Tweak gitlab CI
• [4] 63ZV3FMR Tweak CI
• [5] WNFTZY3M Optionally prevent relevant nix store paths from being GC'ed
• [6] 4U6RHDKN Tweak CI

Change contents

• edit in .gitlab-ci.yml at line 12
  [2.105]→[2.105:127](∅→∅)
  − - nix show-config