SnapshotProvider_EmitsCpuTimeMetric test failing in CI

[ericstj]

I saw this today https://dev.azure.com/dnceng-public/public/_build/results?buildId=1189743&view=ms.vss-test-web.build-test-results-tab&runId=32906332&resultId=107368&paneView=debug

Passes on rerun.

Error message
System.AggregateException : One or more errors occurred. (We shouldn't hit here...)
---- System.InvalidOperationException : We shouldn't hit here...

Stack trace
   at System.Diagnostics.Metrics.MeterListener.RecordObservableInstruments()
   at Microsoft.Extensions.Diagnostics.Metrics.Testing.MetricCollector`1.RecordObservableInstruments() in /_/src/Libraries/Microsoft.Extensions.Diagnostics.Testing/Metrics/MetricCollector.cs:line 267
   at Microsoft.Extensions.Diagnostics.ResourceMonitoring.Windows.Test.WindowsContainerSnapshotProviderTests.SnapshotProvider_EmitsCpuTimeMetric() in /mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring.Tests/Windows/WindowsContainerSnapshotProviderTests.cs:line 238
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
----- Inner Stack Trace -----
   at Moq.Behaviors.ThrowException.Execute(Invocation invocation) in C:\projects\moq4\src\Moq\Behaviors\ThrowException.cs:line 22
   at Moq.SequenceSetup.ExecuteCore(Invocation invocation) in C:\projects\moq4\src\Moq\SequenceSetup.cs:line 35
   at Moq.Setup.Execute(Invocation invocation) in C:\projects\moq4\src\Moq\Setup.cs:line 84
   at Moq.FindAndExecuteMatchingSetup.Handle(Invocation invocation, Mock mock) in C:\projects\moq4\src\Moq\Interception\InterceptionAspects.cs:line 95
   at Moq.Mock.Moq.IInterceptor.Intercept(Invocation invocation) in C:\projects\moq4\src\Moq\Interception\Mock.cs:line 17
   at Moq.CastleProxyFactory.Interceptor.Intercept(IInvocation underlying) in C:\projects\moq4\src\Moq\Interception\CastleProxyFactory.cs:line 107
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at Castle.Proxies.IJobHandleProxy.GetBasicAccountingInfo()
   at Microsoft.Extensions.Diagnostics.ResourceMonitoring.Windows.WindowsContainerSnapshotProvider.GetCpuTime()+MoveNext() in /_/src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/Windows/WindowsContainerSnapshotProvider.cs:line 269
   at System.Diagnostics.Metrics.ObservableInstrument`1.Observe(MeterListener listener)
   at System.Diagnostics.Metrics.MeterListener.RecordObservableInstruments()

[ericstj]

@amadeuszl @evgenyfedorov2