GH-79033: docs: Minor improvement to asyncio.Server.wait_closed()

[Dreamsorcerer]

@gvanrossum Just a small followup from #98582.

In aiohttp, for some reason it was originally written as calling wait_closed() before cancelling the open connections. So, from that wording in the Python documentation I always assumed that it was waiting for the sockets to stop listening, rather than waiting for the connections to be closed. Clearly this was wrong, and it actually did nothing, and aiohttp's shutdown should have been broken long ago.

In particular, the close() method says 'The sockets that represent existing incoming client connections are left open.'.
So, saying that it waits for close() to complete, which itself says connections are left open was a little confusing.

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📚 Documentation preview 📚: https://cpython-previews--111260.org.readthedocs.build/

• Issue: Counter-intuitive behavior of Server.close() / wait_closed() #79033

[gvanrossum]

This phrasing is fine, and we should merge it.

Note, however, that there's another chapter to the wait_closed litany:
#79033 (comment)

[Dreamsorcerer]

Superseded by #111336.