Document that asyncio doesn't support generator-based coroutines

[deadlovelll]

Documentation

asyncio dropped generator-based coroutines in 3.12, but the docs never say so

Proposed fix: state this in the Awaitables section, note the TypeError on create_task(), and add the missing versionchanged:: 3.12 to iscoroutine()

have a fix for that

Linked PRs

• gh-157786: Document that asyncio does not support generator-based coroutines #157787