[rel/17.3] Do not match .NET Standard to Dotnet testhost runner #3958
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Description
.NET Standard is not executable by .NET runner, but in multi TFM we try to execute it which does not work. Instead we should correctly report that there is no runtime provider for it.
Improve error message when testhost crashes to mention the sources that it tried to run.
Related issue
Related #3939
Backport of #3949