fix(tazjin/koptevo): bind quassel on IPv6, too

This should make it possible to use Quassel over Yggdrasil.

Change-Id: Iad81af7c85771928fd50860393d58a14d7878a40
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12502
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

users/tazjin/nixos/koptevo/default.nix

@@ -118,6 +118,7 @@ in
     acmeHost = "koptevo.tazj.in";
     bindAddresses = [
       "0.0.0.0"
+      "::"
     ];
   };