fix(test): add missing _voice_mode attr to GatewayRunner test stubs

tests/gateway/test_background_command.py

@@ -32,6 +32,7 @@ def _make_runner():
     from gateway.run import GatewayRunner
     runner = object.__new__(GatewayRunner)
     runner.adapters = {}
+    runner._voice_mode = {}
     runner._session_db = None
     runner._reasoning_config = None
     runner._provider_routing = {}