fix: remove dead store and no-effect await flagged by CodeQL

- local_converter.py: remove redundant `_default_converter = None` in
  except block of `_ensure_default_converter` (variable was already None,
  re-raised immediately — dead store)
- test_analysis_service.py: replace bare `await task` with
  `await asyncio.gather(task)` to satisfy static analysis

document-parser/infra/local_converter.py

@@ -120,7 +120,6 @@ def _ensure_default_converter() -> DoclingConverter:
         try:
             _default_converter = _build_docling_converter(ConversionOptions())
         except Exception:
-            _default_converter = None
             raise
     return _default_converter
 

document-parser/tests/test_analysis_service.py

@@ -152,7 +152,7 @@ class TestAnalysisServiceCancellation:
         task = asyncio.create_task(instant())
         service._running_tasks["j1"] = task
         task.add_done_callback(functools.partial(service._on_task_done, job_id="j1"))
-        await task
+        await asyncio.gather(task)
 
         assert "j1" not in service._running_tasks