python3Packages.sanic-auth: fix tests (#121279)

After #120881, packages using Sanic's `app.test_client` or
`app.asgi_client` need to depend on `sanic-testing` as well.

pkgs/development/python-modules/sanic-auth/default.nix

···
-{ lib, buildPythonPackage, fetchPypi, sanic, pytestCheckHook }:
+{ lib, buildPythonPackage, fetchPypi, sanic, sanic-testing, pytestCheckHook }:
 
 buildPythonPackage rec {
   pname = "Sanic-Auth";
···
 
   propagatedBuildInputs = [ sanic ];
 
-  checkInputs = [ pytestCheckHook ];
+  checkInputs = [ pytestCheckHook sanic-testing ];
 
   pythonImportsCheck = [ "sanic_auth" ];