lapetus: Clean up old foregejo dumps

hosts/nixos/lapetus/services/forgejo.nix

@@ -55,4 +55,9 @@
       };
     };
   };
+
+  # Clean up dumps older than a week.
+  # The data is also saved in zfs snapshots and rsync backups,
+  # so this is just an extra layer of safety.
+  systemd.user.tmpfiles.rules = [ "d ${config.services.forgejo.stateDir}/dump - - - 7d" ];
 }