Don't add a nix-build build product unless $out is a directory

Dependencies

• [2] PMNWRTGJ Add multiple output support
• [*] OOQ2D3KC * Refactoring: move fetchInput out of hydra_scheduler into a separate
• [*] EDRUQ4UK Die TABs die

Change contents

• edit in src/lib/Hydra/Helper/AddBuilds.pm at line 365
  [2.7028]

  [5.3086]
  + next unless -d $outPath;