Fix hydra-update-gc-roots

Dependencies

• [2] 3D3F5I74 Fix race between hydra-eval-jobs and hydra-update-gc-roots
• [3] WZ3AEJ67 * hydra_update_gc_roots.pl registers build outputs that should be kept
• [4] KJQWSRCC Speed up hydra-update-gc-roots

Change contents

• replacement in src/script/hydra-update-gc-roots at line 133
  [2.261]→[2.261:318](∅→∅)
  − if (lstat($path)->ctime < $now - 24 * 60 * 60) {
  [2.261]

  [2.318]
  + my $st = lstat("$gcRootsDir/$link");

  + if (!defined $st) {

  + print STDERR "skipping link $link: $!\n";

  + } elsif ($st->ctime < $now - 24 * 60 * 60) {