Fix non-mainnet icons

Author: michalrus

nix/internal/launcher-config.nix

@@ -142,7 +142,7 @@ let
   in if networkSupported then supportedNetworks.${network} else unsupported;
 
   iconPath = let
-    networkIconExists = __pathExists (../. + "/installers/icons/${network}");
+    networkIconExists = __pathExists (../../. + "/installers/icons/${network}");
     network' = if networkIconExists then network else "mainnet";
   in {
     small = ../../installers/icons + "/${network'}/64x64.png";