mis-detects curio as asyncio when running in curio in asyncio.to_thread (py3.9)


```python
import curio
import sniffio
import asyncio

async def current_framework():
    return sniffio.current_async_library()


async def amain():
    sniffio.current_async_library()
    return await asyncio.to_thread(curio.run, current_framework)


print(asyncio.run(amain()))  # prints asyncio - should print curio
```