statem: always save sigalgs during PHA

statem: always save sigalgs during PHA

We use the same extension-parsing function on server and client
for convenience, but while the server might worry about tracking
what was previously received and not overwriting it, on the client
receiving a request for post-handshake authentication, we always
want to use the values from the current extension (and should
always have a new session object that we are free to mutate).

It is somewhat unclear whether the server also needs the check
for a resumed connection; it appears to have been added back in
2015 in commit 062178678f5374b09f00d70796f6e692e8775aca as part
of a broad pass to handle extensions on resumption, but without
specific documentation of each extension's handling.

Fixes: #10370
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24651)