detect leaked tasks on tests

[theomonnom]

app        | ==================================== ERRORS ====================================
app        | ____________ ERROR at teardown of test_synthesize_timeout[cartesia] ____________
app        | .venv/lib/python3.9/site-packages/pytest_asyncio/plugin.py:363: in finalizer
app        |     event_loop.run_until_complete(task)
app        | /usr/local/lib/python3.9/asyncio/base_events.py:647: in run_until_complete
app        |     return future.result()
app        | .venv/lib/python3.9/site-packages/pytest_asyncio/plugin.py:354: in async_finalizer
app        |     await gen_obj.__anext__()  # type: ignore[union-attr]
app        | tests/conftest.py:119: in fail_on_leaked_tasks
app        |     pytest.fail(final_msg)
app        | E   Failed: Test leaked resources:
app        | E   
app        | E   Leaked async generators detected:
app        | E     - Async generator with id: 281472563032128
app        | ______________ ERROR at teardown of test_synthesize_timeout[aws] _______________
app        | .venv/lib/python3.9/site-packages/pytest_asyncio/plugin.py:363: in finalizer
app        |     event_loop.run_until_complete(task)
app        | /usr/local/lib/python3.9/asyncio/base_events.py:647: in run_until_complete
app        |     return future.result()
app        | .venv/lib/python3.9/site-packages/pytest_asyncio/plugin.py:354: in async_finalizer
app        |     await gen_obj.__anext__()  # type: ignore[union-attr]
app        | tests/conftest.py:119: in fail_on_leaked_tasks
app        |     pytest.fail(final_msg)
app        | E   Failed: Test leaked resources:
app        | E   
app        | E   Leaked tasks detected:
app        | E   Task Name    : TTS._synthesize_task
app        | E   Coroutine    : ChunkedStream._main_task
app        | E   Location     : /app/livekit-agents/livekit/agents/tts/tts.py:203
app        | E   State        : pending
app        | E   
app        | E   Task Name    : TTS._metrics_task
app        | E   Coroutine    : ChunkedStream._metrics_monitor_task
app        | E   Location     : /app/livekit-agents/livekit/agents/tts/tts.py:164
app        | E   State        : pending
app        | E   
app        | E   Leaked async generators detected:
app        | E     - Async generator with id: 281473126488096
app        | E     - Async generator with id: 281473126487952