fix(tests): mark OpenAI-dependent test as api_key_required to prevent CI failures

src/backend/tests/unit/api/v1/test_mcp_client_server.py

@@ -436,6 +436,7 @@ edges:
         with pytest.raises(ValueError, match="unknown target 'Z'"):
             await mcp_server_module.create_flow_from_spec(spec)
 
+    @pytest.mark.api_key_required
     async def test_create_flow_from_spec_prompt_template_variables(self):
         """Prompt Template with {var} in template creates dynamic input fields."""
         spec = """\