Fix "build_with_fsharp_from_mono" CI lane

Somehow, the "ResolveReferences" target was not found anymore by
the msbuild tool used in this lane, but we don't need this target
when using Mono because this workaround is only used when using
"dotnet" to create the nuget package.

Author: knocte

src/DotNetLightning.Core/DotNetLightning.Core.fsproj

@@ -102,7 +102,11 @@
     <PackageReference Include="System.Memory" Version="4.5.3" />
   </ItemGroup>
 
-  <Target Name="CopyProjectReferencesToPackage" DependsOnTargets="ResolveReferences">
+  <!-- this is a workaround only needed for nuget push (so, not Mono, but just "dotnet nuget"), for more info see
+       https://github.com/joemphilips/DotNetLightning/issues/14 and https://github.com/joemphilips/DotNetLightning/commit/c98307465f647257df1438beadb4cabc7db757f2
+       and https://github.com/joemphilips/DotNetLightning/issues/14 and https://github.com/NuGet/Home/issues/3891#issuecomment-377319939 -->
+  <Target Name="CopyProjectReferencesToPackage" DependsOnTargets="ResolveReferences"
+          Condition="'$(MSBuildRuntimeType)'!='Mono'">
     <ItemGroup>
       <BuildOutputInPackage Include="@(ReferenceCopyLocalPaths-&gt;WithMetadataValue('ReferenceSourceTarget', 'ProjectReference'))" />
     </ItemGroup>