test: 修复 CI GPU 环境下 lipsync 测试走 GPU 路径导致 call_args 为 None

CI 环境 USE_GPU_LIPSYNC=true，MagicMock 的 has_available_worker() 返回 truthy MagicMock，
导致 create_job 走 GPU 路径提前 return，submit_lipsync 未被调用，3 个依赖 MediaKit
路径的测试失败：
- test_create_job_api_failure: 未抛 MediaKitError
- test_create_job_direct_audio_skips_tts: submit_lipsync.call_args 为 None
- test_create_job_resigns_oss_urls_before_submit: 同上

在测试中显式设置 svc.settings.use_gpu_lipsync = False，强制走 MediaKit 路径验证相关逻辑。

tests/unit/test_lipsync_routes.py

@@ -298,6 +298,7 @@ class TestLipsyncServiceUnit:
 
         mock_db = MagicMock()
         svc = LipsyncService(mock_db, client=mock_mediakit)
+        svc.settings.use_gpu_lipsync = False
 
         with pytest.raises(MediaKitError, match="API 调用失败"):
             svc.create_job(
@@ -473,6 +474,7 @@ class TestLipsyncServiceUnit:
             cosyvoice_service=mock_cosyvoice,
             voice_clone_repo=MagicMock(),
         )
+        svc.settings.use_gpu_lipsync = False
         job = svc.create_job(
             user_id="user-1",
             video_url="https://example.com/video.mp4",
@@ -616,12 +618,14 @@ class TestSignMediaUrl403Fix:
     def _svc(self, mock_mediakit, mock_cosyvoice):
         from app.services.lipsync_service import LipsyncService
 
-        return LipsyncService(
+        svc = LipsyncService(
             MagicMock(),
             client=mock_mediakit,
             cosyvoice_service=mock_cosyvoice,
             voice_clone_repo=MagicMock(),
         )
+        svc.settings.use_gpu_lipsync = False
+        return svc
 
     def test_own_oss_unsigned_url_gets_resigned(self, mock_mediakit, mock_cosyvoice):
         """裸 public_url（不带签名，私有桶匿名 403）必须被重签."""