modules/nixos/hydra: fix hydra-compress-logs

this is the default but we need to set it explictly as it is currently broken upstream and in nixpkgs

modules/nixos/hydra.nix

@@ -48,6 +48,7 @@
         evaluator_workers = 8
         max_concurrent_evals = 2
         max_output_size = ${builtins.toString (8 * 1024 * 1024 * 1024)}
+        compress_build_logs_compression = bzip2
       '';
     };