Fix deadlock in TestUtilities.TestEventListener

[rzikm]

I hit this surprisingly often and mistook it for test hang. From a dotnet dump

First callstack
                   1 System.Threading.Monitor.Enter(Object, Boolean ByRef)             // waits for TestEventListener (instance)
                   1 TestUtilities.TestEventListener.OnEventSourceCreated(EventSource)
                   1 System.Diagnostics.Tracing.EventSource.AddListener(EventListener) // holds EventListener.EventListenersLock
                   1 System.Diagnostics.Tracing.EventListener.AddEventSource(EventSource)
                   1 System.Diagnostics.Tracing.EventSource.Initialize(Guid, String, String[])
                   1 System.Diagnostics.Tracing.EventSource..ctor(EventSourceSettings, String[])
                   1 System.Diagnostics.Tracing.EventSource..ctor(EventSourceSettings)
                   1 System.Diagnostics.Tracing.EventSource..ctor()
                   1 System.Net.NameResolutionTelemetry..ctor()
                   1 System.Net.NameResolutionTelemetry..cctor()
                   1 System.Net.Dns.RunAsync(Func<Object,Int64,__Canon>, Object, CancellationToken)

second callstack
                   1 System.Threading.Monitor.Enter(Object, Boolean ByRef)             // wait for EventListener.EventListenersLock
                   1 System.Diagnostics.Tracing.EventSource.SendCommand(EventListener, EventProviderType, Int32, EventCommand, Boolean, EventLevel, EventKeywords, IDictionary<String,String>)
                   1 System.Diagnostics.Tracing.EventListener.EnableEvents(EventSource, EventLevel, EventKeywords, IDictionary<String,String>)
                   1 System.Diagnostics.Tracing.EventListener.EnableEvents(EventSource, EventLevel, EventKeywords)
                   1 System.Diagnostics.Tracing.EventListener.EnableEvents(EventSource, EventLevel)
                   1 TestUtilities.TestEventListener.OnEventSourceCreated(EventSource)
                   1 TestUtilities.TestEventListener..ctor(Action<String>, String[])   // holds TestEventListener (instance)
                   1 TestUtilities.TestEventListener..ctor(ITestOutputHelper, String[])

Simply not holding the lock (this) for so long should be enough.

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[CarnaViire]

We don't do a second pass now, do we? You've removed the OnEventSourceCreated call...

[CarnaViire]

Ah, I see from the callstack above, scratch that

[MihaZupan]

Nice catch