Register restarted derivations as GC roots

Dependencies

• [2] VHV6GI4L Add a jobset eval action to restart all aborted/cancelled builds
• [*] 2GK5DOU7 * Downloading closures.

Change contents

• edit in src/lib/Hydra/Helper/Nix.pm at line 577
  [2.1101]

  [2.1101]
  +

  + registerRoot $build->drvpath;