XEvent tests intermittent failures

[paulmedynski]

We're seeing intermittent failures during CI test runs:

[xUnit.net 00:00:04.93]     Microsoft.Data.SqlClient.ManualTesting.Tests.XEventsTracingTest.XEventActivityIDConsistentWithTracing(query: "sp_help", commandType: StoredProcedure, xEvent: "rpc_starting") [FAIL]
  [xUnit.net 00:00:04.93]       Assert.Equal() Failure: Values differ
  [xUnit.net 00:00:04.93]       Expected: 1
  [xUnit.net 00:00:04.93]       Actual:   0
  [xUnit.net 00:00:04.93]       Stack Trace:
  [xUnit.net 00:00:04.93]         /_/src/Microsoft.Data.SqlClient/tests/ManualTests/TracingTests/XEventsTracingTest.cs(67,0): at Microsoft.Data.SqlClient.ManualTesting.Tests.XEventsTracingTest.GetCommandActivityId(String commandText, String eventName, Guid connectionId, XmlDocument xEvents)
  [xUnit.net 00:00:04.93]         /_/src/Microsoft.Data.SqlClient/tests/ManualTests/TracingTests/XEventsTracingTest.cs(51,0): at Microsoft.Data.SqlClient.ManualTesting.Tests.XEventsTracingTest.XEventActivityIDConsistentWithTracing(String query, CommandType commandType, String xEvent)
  [xUnit.net 00:00:04.93]            at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
  [xUnit.net 00:00:04.93]            at System.Reflection.MethodBaseInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs, BindingFlags invokeAttr)
    Failed Microsoft.Data.SqlClient.ManualTesting.Tests.XEventsTracingTest.XEventActivityIDConsistentWithTracing(query: "sp_help", commandType: StoredProcedure, xEvent: "rpc_starting") [1 s]

These tests run commands against SQL Server instances and capture events. I suspect some timing issues.

[edwardneal]

This is one of the tests I wrote - apologies. It looks like XEvents are written to the target asynchronously, and if the SQL Server is under load then this can preempt the next query.

I'll submit a PR tomorrow which accounts for the timing issue.