hosts: nixos: porthos: fix tmux 24-bit color

Well at least this fixes it for the usual client (my laptop).

hosts/nixos/porthos/home.nix

@@ -1,6 +1,12 @@
 { ... }:
 {
   my.home = {
+    # Allow using 24bit color when SSH-ing from various clients
+    tmux.trueColorTerminals = [
+      # My usual terminal, e.g: on laptop
+      "alacritty"
+    ];
+
     # Always start a tmux session when opening a shell session
     zsh.launchTmux = true;
   };