Remove un-necessary socket requirements in `contextlib` async tests

[graingert]

Proposal:

the contextlib async tests should run coroutines using coro.send(None) because they don't need an async framework to run. This would remove asyncio from the tests and support running on emscripten/wasi

Linked PRs

• gh-128234: support emscripten and wasi in async contextlib tests, by removing asyncio from contextlib async tests #95888