* Update System.Runtime.CompilerServices.Unsafe to 4.7.1

This brings it up to the latest stable version on nuget.org so we can keep updating other dependencies in VS without fear that they need a dependency that's newer than what VS ships.

* Update System.Threading.Tasks.Extensions to 4.5.4

This matches a VS update recently made: https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequest/265216?path=%2Fsrc%2FSetupPackages%2FCoreIde%2FMinShell%2Fcore%2Ffiles.swr&_a=commits

* Update System.Threading.Tasks.Dataflow and Microsoft.Bcl.AsyncInterfaces

These bring up more corefx assemblies to match the version inserted to VS as of https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequest/265216?path=%2Fsrc%2FSetupPackages%2FCoreIde%2FMinShell%2Fcore%2Ffiles.swr&_a=commits.

* Skip CommandLineRunnerTests.TestReferenceDirective
Co-authored-by: NRikki Gibson <rikkigibson@gmail.com>