preventing asyncio.CancelledError from disrupting the request handling without marking the connection as failed

[rafaelfelix]

attempts to address the issue reported in https://github.com/encode/httpx/issues/2139#issuecomment-1075307982

feel free to take over and make it a more complete patch, this is what I did locally and worked. just wanted to share the approach :)

[zanieb]

I believe this also addresses https://github.com/encode/httpcore/issues/564

[tomchristie]

feel free to take over and make it a more complete patch

Thank you, yes. Closing as superseded by #580