test: restore test that was skipped due to Colang 2.0 serialization issue (#1449)

Author: Pouyanpi

tests/v2_x/test_passthroug_mode.py

@@ -81,9 +81,6 @@ def test_passthrough_llm_action_not_invoked_via_logs(self):
             self.assertIn("content", response)
             self.assertIsInstance(response["content"], str)
 
-    @unittest.skip(
-        reason="Github issue https://github.com/NVIDIA/NeMo-Guardrails/issues/1378"
-    )
     def test_passthrough_llm_action_invoked_via_logs(self):
         chat = TestChat(
             config,