A warning regarding enabling NixOS containers and virtualisation.containers at the same time with state versions < 22.05 had been added in commit 3c49151f154a3872eb278c214863d926a4f8abf6. But this warning had accidentally been defined in the wrong place, and the warning has therefore not actually been in effect. This commit fixes that.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.