flake: dummy options for extra-container 26.11 compatibility
nixpkgs 26.11 systemd.nix now reads environment.variables.SYSTEMD_XKB_DIRECTORY
and config.i18n.imperativeLocale, but extra-container's minimal module set
omits the modules that declare them, breaking the container-virtulus eval in
`nix flake check`. Add dummy options to the existing workaround block.
Assisted-by: Claude Code (claude-opus-4-8[1m])