knossosnet: fix intermittent build failure (#491045)

pkgs/by-name/kn/knossosnet/package.nix

@@ -25,6 +25,9 @@ buildDotnetModule rec {
   nugetDeps = ./deps.json;
   executables = [ "Knossos.NET" ];
 
+  # IO errors in build due to solution building race
+  enableParallelBuilding = false;
+
   runtimeDeps = [ openal ];
 
   nativeBuildInputs = [ copyDesktopItems ];