python3Packages.bork: fix build

The `bork` build broke when `build` [updated], so this commit un-borks `bork` by relaxing the build requirement on `build`.

Yes, I do think I'm clever, why do you ask?

[updated]: e1338b7267

pkgs/development/python-modules/bork/default.nix

@@ -34,6 +34,7 @@ buildPythonPackage rec {
   ];
 
   pythonRelaxDeps = [
+    "build"
     "packaging"
     "urllib3"
   ];