Fix ServerVersion issue

Summary: Now SingleStoreConnection returns version of S2, not MySQL. Updated tests to correspond changes

Test Plan: https://app.circleci.com/pipelines/github/memsql/SingleStoreNETConnector/231/workflows/de2d437f-7d50-4b8e-85c0-0c395bdfc5ab

Reviewers: pmishchenko-ua

Reviewed By: pmishchenko-ua

Subscribers: engineering-list

JIRA Issues: PLAT-6324

Differential Revision: https://grizzly.internal.memcompute.com/D58353

src/SingleStoreConnector/SingleStoreConnection.cs

@@ -491,6 +491,8 @@ public override string ConnectionString
 
 	public override string ServerVersion => Session.MySqlCompatVersion.OriginalString;
 
+	public string S2ServerVersion => Session.S2ServerVersion.OriginalString;
+
 	/// <summary>
 	/// The connection ID from SingleStore Server.
 	/// </summary>