Unstable test: HangReportNotSuppressedOnLongRunningTaskJoinCancelled

[AArnott]

The HangReportNotSuppressedOnLongRunningTaskJoinCancelled test failed on appveyor:

    HangReportNotSuppressedOnLongRunningTaskJoinCancelled [FAIL]
      Assert.True() Failure
      Expected: True
      Actual:   False
      Stack Trace:
        src\Microsoft.VisualStudio.Threading.Tests\JoinableTaskContextTests.cs(324,0): at Microsoft.VisualStudio.Threading.Tests.JoinableTaskContextTests.HangReportNotSuppressedOnLongRunningTaskJoinCancelled()

[AArnott]

and again

2018-11-10T07:40:29.5985071Z Failed   HangReportNotSuppressedOnLongRunningTaskJoinCancelled
2018-11-10T07:40:29.5985662Z Error Message:
2018-11-10T07:40:29.5985866Z  Assert.True() Failure
2018-11-10T07:40:29.5986001Z Expected: True
2018-11-10T07:40:29.5986132Z Actual:   False
2018-11-10T07:40:29.5986296Z Stack Trace:
2018-11-10T07:40:29.5986649Z    at Microsoft.VisualStudio.Threading.Tests.JoinableTaskContextTests.HangReportNotSuppressedOnLongRunningTaskJoinCancelled() in D:\a\1\s\src\Microsoft.VisualStudio.Threading.Tests\JoinableTaskContextTests.cs:line 324

[AArnott]

and again:

2018-12-01T19:03:51.1915399Z [xUnit.net 00:07:36.4405858]     HangReportNotSuppressedOnLongRunningTaskJoinCancelled [FAIL]
2018-12-01T19:03:51.2039601Z [xUnit.net 00:07:36.4424245]       Assert.True() Failure
2018-12-01T19:03:51.2040677Z [xUnit.net 00:07:36.4425061]       Expected: True
2018-12-01T19:03:51.2041118Z [xUnit.net 00:07:36.4425468]       Actual:   False
2018-12-01T19:03:51.2041501Z [xUnit.net 00:07:36.4432549]       Stack Trace:
2018-12-01T19:03:51.2042171Z [xUnit.net 00:07:36.4468306]         src\Microsoft.VisualStudio.Threading.Tests\JoinableTaskContextTests.cs(324,0): at Microsoft.VisualStudio.Threading.Tests.JoinableTaskContextTests.HangReportNotSuppressedOnLongRunningTaskJoinCancelled()