electrum: fix build with protobuf dependency

Since the update to version 5 with
https://github.com/NixOS/nixpkgs/commit/7cdaa0b80c9da64b2acb6cc8e8f73d2f4489aaeb ,
the `python3Packages.protobuf` package
no longer provides the `protoc` program.
Instead, one has to add the `protobuf` package
(not the python package) directly.

pkgs/applications/misc/electrum/default.nix

@@ -2,6 +2,7 @@
 , stdenv
 , fetchurl
 , fetchFromGitHub
+, protobuf
 , wrapQtAppsHook
 , python3
 , zbar
@@ -70,7 +71,7 @@ python.pkgs.buildPythonApplication {
     cp -ar ${tests} $sourceRoot/tests
   '';
 
-  nativeBuildInputs = lib.optionals enableQt [ wrapQtAppsHook ];
+  nativeBuildInputs = [ protobuf ] ++ lib.optionals enableQt [ wrapQtAppsHook ];
   buildInputs = lib.optional (stdenv.hostPlatform.isLinux && enableQt) qtwayland;
 
   propagatedBuildInputs = with python.pkgs; [