nixos: Fix build of manual
nixos: Fix build of manual

Manual build broken by 79f7f89442d9132c35b6417187cb1567eca2b910, which
is part of pull request #59179 (Fix Cassandra, improve config and
tests).

The issue was just a small error because of an unbalanced <literal/>
tag, so only a "/" was missing :-)

Signed-off-by: aszlig <ee1aa092358634f9c53f01b5a783726c9e21b35a@nix.build>
Cc: da39a3ee5e6b4b0d3255bfef95601890afd80709@aanderse

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs