nixos/hydra: gc-check-reachability no longer exists in nix 2.4 (#117925)

* nixos/hydra: gc-check-reachability no longer exists in nix 2.4

fixup! nixos/hydra: gc-check-reachability no longer exists in nix 2.4

* Update nixos/modules/services/continuous-integration/hydra/default.nix

Co-authored-by: Sandro <sandro.jaeckel@gmail.com>

Co-authored-by: Sandro <sandro.jaeckel@gmail.com>

Changed files
+2
nixos
modules
services
continuous-integration
hydra
+2
nixos/modules/services/continuous-integration/hydra/default.nix
···
keep-outputs = true
keep-derivations = true
+
+
'' + optionalString (versionOlder (getVersion config.nix.package.out) "2.4pre") ''
# The default (`true') slows Nix down a lot since the build farm
# has so many GC roots.
gc-check-reachability = false