Use documented assertion method

I can't even find documentation for the `called_with` attribute anymore.

The proper one seems to be `Mock.assert_called_with()` or inspecting
`Mock.call_args` directly.

See also:
https://docs.python.org/3.12/library/unittest.mock.html#unittest.mock.Mock.assert_called_with

laces/tests/test_templatetags/test_laces.py

@@ -38,7 +38,7 @@ def render_parent_template_with_context(self, context: dict):
         return self.parent_template.render(Context(context))
 
     def assertRenderHTMLCalledWith(self, context: dict):
-        self.assertTrue(self.component.render_html.called_with(Context(context)))
+        self.component.render_html.assert_called_with(Context(context))
 
     def test_render_html_return_in_parent_template(self):
         self.assertEqual(self.component.render_html(), "Rendered HTML")