fix(tests): suppress deprecation error of event_loop

[natsukium]

The event_loop of pytest-asyncio should be closed explicitly, as shown in the following document.
https://github.com/pytest-dev/pytest-asyncio/tree/v0.18.3#event_loop
As of 0.18.3, which is fixed in pyproject.toml, it closes automatically, but as of 0.21.0, it throws an error.

It would be good to fix this for future updates.

[rattrayalex]

Thanks for reporting & fixing! This looks right at first blush; we'll take a deeper look at this tomorrow.

[RobertCraigie]

Thanks for the fix @natsukium! We've pushed a fix separately that includes your changes and also bumps pytest-asyncio to the latest version in #114.

[natsukium]

thanks!