Error publishing .snupkg files - The required element 'authors' is missing

[rmunn]

#407 got the AppVeyor build running again, but now there's an error:

Error publishing NuGet package artifact output/SIL.ChorusPlugin.LibFLExBridge.4.2.0-beta0025.snupkg: NuGet package cannot be read: The required element 'authors' is missing from the manifest.

And the same error message for all other symbol packages: SIL.ChorusPlugin.LibTriboroughBridge, SIL.ChorusPlugin.FLEx, etc.

This may become moot if #405 is approved and nuget package building moves to GitHub Actions, but in the meantime, it's worth looking into this error.

[rmunn]

Directory.Build.props contains <Authors>SIL International</Authors>, so it's possible that this is a bug in the process of building the symbols package rather than an actual missing value.