fixes for nix on droid tmux doesn't start

[mio-19]

nix-config/hosts/pixel7a/home-nix-on-droid.nix

Line 34 in 99f23e4

tmux.enable = lib.mkForce false;

This is my fix

  environment.sessionVariables.SHELL = "${pkgs.zsh}/bin/zsh"; # fix tmux [exited] problem