Tests: fixed extracting QUIC early secret if PSK is not in use. Although, PSK binder values in the pre-shared key extension are constructed with a binder key derived from the early secret extracted with input keying material of the corresponding offered PSK, an actual early secret should be recomputed with a selected PSK. See RFC 8446, section 7.1 and 4.2.11.2. Seen with QuicTLS and disabled session tickets, which, unlike in BoringSSL, still sends session tickets but doesn't accept any pre-shared keys.