Forwarded request #1045069 from bnavigator

- Update to 0.16.3
* Allow ws and wss schemes. Allows us to properly support
websocket upgrade connections. (#625)
* Forwarding HTTP proxies use a connection-per-remote-host.
Required by some proxy implementations. (#637)
* Don't raise RuntimeError when closing a connection pool with
active connections. Removes some error cases when cancellations
are used. (#631)
* Lazy import anyio, so that it's no longer a hard dependancy,
and isn't imported if unused. (#639)
- Add httpcore-allow-deprecationwarnings-test.patch
gh#encode/httpcore#511, gh#agronholm/anyio#470