test(robot-server): replace pytest-aiohttp with pytest-asyncio

[mcous]

Overview

robot-server follow-up for #9981. Less important / impactful than that PR, but still important to unblock some dev environment improvements that are a little bit blocked by the fact that various dev environments pull in aiohttp completely unnecessarily.

That being said, still seeing a non-trivial test suite speedup:

• This PR: 1m39s
• edge: 2m21s

Changelog

• test(robot-server): replace pytest-aiohttp with pytest-asyncio

Review requests

• Keep an eye out for any test freezing like what we say with test(api): Replace pytest-aiohttp with pytest-asyncio for running async tests #9981
• Changes to tests make sense

Risk assessment

Low risk to production, test-only changes. Risk is to DX, since we could be unintentionally adding flakiness to our test suite locally and in CI. However, if things go well, this is a DX improvement.

[amitlissack]

Lovely