_close_expire_connections is unexpectedly expensive with tls connections

[bdraco]

It looks like the cause is calling into anyio get_extra_info because this function does a lot of work under the hood https://github.com/agronholm/anyio/blob/e0529a31e819064fcf1eaf7df55d1712a30bed6b/src/anyio/streams/tls.py#L230

All that httpcore wants is is_readable

httpcore/httpcore/_async/http11.py

Line 290 in 5518172

and self._network_stream.get_extra_info("is_readable")

but it looks like the extra call results in a few bonus calls that get thrown away