Fix memory leak in tls_parse_ctos_psk()

Fix memory leak in tls_parse_ctos_psk()

`sess` is not NULL at this point, and is freed on the success path, but
not on the error path. Fix this by going to the `err` label such that
`SSL_SESSION_free(sess)` is called.

CLA: trivial

Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25643)