Fix intermittent Windows and Cygwin failures in s_server

Fix intermittent Windows and Cygwin failures in s_server

The same kind of failure that has already been observed on the
s_client can sometimes also be observed on s_server, so we need to add
the same kind of 50ms delay as was previously added on s_client.

Ref: git commit cb2e10f257a464c6b475b321dd9e4769df84dbf6:

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5079)