Remove deprecated OpenSSH configuration options from ci/test.sh:
- Protocol 2 (deprecated since OpenSSH 7.4)
- RSAAuthentication (deprecated since OpenSSH 7.4)
- ChallengeResponseAuthentication (deprecated since OpenSSH 9.6)
- HostCertificate pointing to .pub file (invalid configuration)
- Duplicate HostKey directive

These options were causing warnings with OpenSSH 10.0 in Fedora Rawhide
and preventing SSH tests from functioning properly.

Tested with OpenSSH 10.0p2 on Fedora Rawhide.

…C for submodules

Fixes #6963

Update our CI to use poxygit v0.8.1, which has additional mocking and
debugging capabilities.

As part of this, the paths to the `speed` test routes changed - now they
are `speed:<n>` where `<n>` is the speed to emulate in bps.

poxygit now supports a "specification" within the URI that can provide
additional details about the mock/debugging connection. The `:none`
suffix on the redirect request indicates that the proxy should send a 0
byte response body.

When we were done reading headers, we checked if we needed to read a
body, or if we were done. The body check was done by looking at the
transfer encoding type and the content type. If we were chunked, then we
know we have a body (it may be a zero byte body, but we would need to
read the chunk length to know this). But looking at the content _type_
was erroneous; we should have been looking at the content _length_.

The effect of this is that when a server sends a zero byte response
with a content _type_, we try to go read the body, which does not exist.
We will hang waiting for the body that the server will never send.

Correct this typo. Now we will try to read the body if there was a
content _length_ specified, or if the transfer encoding is chunked.