CSHARP-3303: Monitor_sleep_at_least_minHeartbeatFreqencyMS_between_checks pickup pick up single server from connection string

Author: BorisDog

tests/MongoDB.Driver.Tests/Specifications/server-discovery-and-monitoring/ServerDiscoveryAndMonitoringProseTests.cs

@@ -96,6 +96,7 @@ public void Monitor_sleep_at_least_minHeartbeatFreqencyMS_between_checks()
                 }}");
 
             var settings = DriverTestConfiguration.GetClientSettings();
+            settings.Servers = new[] { settings.Servers.First() };
 
             // set settings.DirectConnection = true after removing obsolete ConnectionMode
 #pragma warning disable CS0618 // Type or member is obsolete