System.IO.Tests.*.DoesntExistThenCreate_ReturnsDefaultValues fails on CI

[ViktorHofer]

• DoesntExistThenCreate_ReturnsDefaultValues

https://mc.dot.net/#/user/dotnet-bot/pr~2Fdotnet~2Fcorefx~2Frefs~2Fpull~2F38676~2Fmerge/test~2Ffunctional~2Fcli~2Finnerloop~2F/20190701.40/workItem/System.IO.FileSystem.Tests

[ericstj]

Missing piece of data here: test has existed in codebase for some time but was missing Fact attribute. When Fact was added it started running & failing. /cc @JeremyKuhne dotnet/corefx#38676