fix(tests): satisfy mypy on the queue-item push tests

The #568 tests unpacked AsyncMock.await_args without narrowing its
Optional type and passed a SimpleNamespace where _format_task_detail
is annotated TaskTable. Narrow with the repo-standard 'assert
await_args is not None' and cast the fake task at the call sites.

tests/unit/services/test_release_manager_engine.py

@@ -238,6 +238,7 @@ async def test_proposes_sends_telegram_push(
     task = await engine.run_cycle()
     assert task is not None
     notify.assert_awaited_once()
+    assert notify.await_args is not None
     _args, kwargs = notify.await_args
     assert kwargs["kind"] == "release"
     assert kwargs["id8"] == str(task.id)[:8]