Add a test to check .NET uses the system config cipher suites

[omajid]

Some changes were done upstream: dotnet/runtime#39359

We need some tests to make sure they are still working (correctly) for all future releases of .NET and the Linux distro.

[tmds]

We could try write a test that makes SslStream negotiate to something other than what is in the hard-coded list.
The negotiated ciphersuite can be retrieved using SslStream.NegotiatedCipherSuite.