attic: add missing dependency on 'llfuse'

Without this one cannot mount the backup repository:

$ attic mount /backups/backup.attic mnt
attic: the "llfuse" module is required to use this feature
attic: Exiting with failure status due to previous errors

Changed files
+1 -1
pkgs
tools
backup
attic
+1 -1
pkgs/tools/backup/attic/default.nix
···
};
propagatedBuildInputs = with python3Packages;
-
[ cython msgpack openssl acl ];
+
[ cython msgpack openssl acl llfuse ];
preConfigure = ''
export ATTIC_OPENSSL_PREFIX="${openssl}"