Silent fail on missing license

[mswehli]

Hi,

Just came across an small issue, but when the license file isn't included for the project, and so the NuGet pack step fails, the action still registers it as a success. So below is a cutout of the output for a small project i have on github, as you can see the build succeeds, but the pack fails, and the push fails.

`--------------------------------------------------------------------------------------
Microsoft (R) Build Engine version 16.5.0+d4cbfca49 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

Restore completed in 742.19 ms for /home/runner/work/moodio/moodio/Moodio.Common/Moodio.Common.csproj.
Moodio.Common -> /home/runner/work/moodio/moodio/Moodio.Common/bin/Release/netstandard2.0/Moodio.Common.dll

Build succeeded.
0 Warning(s)
0 Error(s)

Time Elapsed 00:00:14.06
Microsoft (R) Build Engine version 16.5.0+d4cbfca49 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

/usr/share/dotnet/sdk/3.1.201/Sdks/NuGet.Build.Tasks.Pack/build/NuGet.Build.Tasks.Pack.targets(198,5): error NU5030: The license file 'LICENSE' does not exist in the package. [/home/runner/work/moodio/moodio/Moodio.Common/Moodio.Common.csproj]
Generated Package: undefined
error: File does not exist (undefined).

`

[brandedoutcast]

Thanks for reporting it, rest assured