[Exporter.Geneva] Fix user event unit tests failures on .NET 9

[xiang17]

          Consider creating separate issue and link them in the code.

Originally posted by @Kielek in #2316 (comment)

Two test cases were tagged as skip due to failure after the SDK is bumped to 9.0:

opentelemetry-dotnet-contrib/test/OpenTelemetry.Exporter.Geneva.Tests/UnixUserEventsDataTransportTests.cs

Lines 52 to 144 in 3c6cf48

	[Fact(Skip = "This would fail on Ubuntu. Skipping for now.")]
	public void UserEvents_Enabled_Success_Linux()
	{
	EnsureUserEventsEnabled();
	var listener = new PerfTracepointListener(
	MetricUnixUserEventsDataTransport.MetricsTracepointName,
	MetricUnixUserEventsDataTransport.MetricsTracepointNameArgs);
	if (listener.IsEnabled())
	{
	throw new NotSupportedException($"{MetricUnixUserEventsDataTransport.MetricsTracepointName} is already enabled");
	}
	try
	{
	listener.Enable();
	MetricUnixUserEventsDataTransport.Instance.SendOtlpProtobufEvent(
	testRequest,
	testRequest.Length);
	Thread.Sleep(5000);
	foreach (var e in listener.Events)
	{
	this.testOutputHelper.WriteLine(string.Join(", ", e.Select(kvp => $"{kvp.Key}={kvp.Value}")));
	}
	Assert.Single(listener.Events);
	var @event = listener.Events[0];
	Assert.EndsWith($" ({MetricUnixUserEventsDataTransport.MetricsProtocol})", @event["protocol"]);
	Assert.Equal(MetricUnixUserEventsDataTransport.MetricsVersion, @event["version"]);
	var eventBufferStringData = @event["buffer"].AsSpan();
	byte[] eventBuffer = new byte[(eventBufferStringData.Length + 1) / 3];
	var index = 0;
	var position = 0;
	while (position < eventBufferStringData.Length)
	{
	eventBuffer[index++] = byte.Parse(eventBufferStringData.Slice(position, 2), NumberStyles.HexNumber);
	position += 3;
	}
	Assert.Equal(testRequest, eventBuffer);
	}
	finally
	{
	try
	{
	listener.Disable();
	}
	catch
	{
	}
	listener.Dispose();
	}
	}
	[Fact(Skip = "This would fail on Ubuntu. Skipping for now.")]
	public void UserEvents_Disabled_Success_Linux()
	{
	EnsureUserEventsEnabled();
	var listener = new PerfTracepointListener(
	MetricUnixUserEventsDataTransport.MetricsTracepointName,
	MetricUnixUserEventsDataTransport.MetricsTracepointNameArgs);
	if (listener.IsEnabled())
	{
	throw new NotSupportedException($"{MetricUnixUserEventsDataTransport.MetricsTracepointName} is already enabled");
	}
	try
	{
	MetricUnixUserEventsDataTransport.Instance.SendOtlpProtobufEvent(
	testRequest,
	testRequest.Length);
	Thread.Sleep(5000);
	Assert.Empty(listener.Events);
	}
	finally
	{
	listener.Dispose();
	}
	}