Add a test to validate our new SSL_accept connection objects

Add a test to validate our new SSL_accept connection objects

Quick test to validate that:

a) our new pending SSL accept callback works
and
b) That our callback passed SSL objects match those that are returned
by SSL_accept_connection

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26361)